Hello,
My 7A has a gascolator that's basically inaccessible to drain during pre-flight. Do you all sump your gascolators?
My 7A has a gascolator that's basically inaccessible to drain during pre-flight. Do you all sump your gascolators?
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Do you sump your gascolator?
- Thread starter SwimmingDragon518
- Start date
If you have a gascolator, it needs to be "sumped" before first flight of the day.
Always
It’s a very important precaution. A flight instructor here was killed a few years ago due to water in the fuel tanks of a Tecnam.
It’s a very important precaution. A flight instructor here was killed a few years ago due to water in the fuel tanks of a Tecnam.
BoydBirchler
Well Known Member
My RV7 originally had a gascolator. It was useless! It would not drain fuel unless I would turn on the boost pump.
When I changed to fuel injection I eliminated it and replaced it with an AFP high pressure boost pump, with a high flow fliter. The filter gets serviced at each condition inspection.
I sump the lowest point in my taildragger's fuel system: which is each tank's rear inboard main tank drains.
There are a lot of us out here that feel the placement of a gascolator ahead of the firewall, in that hot environment, is perfect for boiling fuel and causing vaporlock.
When I changed to fuel injection I eliminated it and replaced it with an AFP high pressure boost pump, with a high flow fliter. The filter gets serviced at each condition inspection.
I sump the lowest point in my taildragger's fuel system: which is each tank's rear inboard main tank drains.
There are a lot of us out here that feel the placement of a gascolator ahead of the firewall, in that hot environment, is perfect for boiling fuel and causing vaporlock.
Jesus you guys are frightening me. Should I get rid of the gascolator?
That would certainly be an option, as long as you retained the ability to sump the lowest part of your fuel system.
I confess I'm a little baffled at the concept of not sumping the gascolator as an utterly routine part of the pre-flight. I've never found water in a gascolator either, but I've never translated that to meaning I don't need to check the rudder bolts or aileron/flap jam nuts just because I've never found them to be loose.
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every pre-flight inspection
Having owned a Mooney M20e for years found sumping the gascolator was a royal pain, having to climb into the cockpit each time, just to pull the little actuator ring on the pilot side floor to clear any water/debris that may have collected in the gascolator. Always, it came back clean.
Having gotten tired of this exercise each preflight, rationalized that checking the wing tank drains each time before flight would catch any contaminates, before they found their way to the gascolator. Wrong!
Apparently fuel injected engines are not tolerant of anything other than 100% clean fuel. It was no fun having the always smooth running engine start stumbling in the downwind leg to land. Luckily the loss of power was near a runway.
I mentioned my engine issue to an old timer pilot that has forgotten more than I can ever hope to learn and his first comment was, 'did you sump the gascolator?'
There was a wee bit of water/gunk had accumulated. Thereafter, I would not be comfortable to fly without first checking the gascolator.
The RV3 I now fly is carbed and maybe more tolerant of contaminates in the fuel? Though I have to turn the boost pump on then get down on my backside flat out on the floor to access the gascolator, would not consider flying without checking the gascolator.
My 2 cents
Having owned a Mooney M20e for years found sumping the gascolator was a royal pain, having to climb into the cockpit each time, just to pull the little actuator ring on the pilot side floor to clear any water/debris that may have collected in the gascolator. Always, it came back clean.
Having gotten tired of this exercise each preflight, rationalized that checking the wing tank drains each time before flight would catch any contaminates, before they found their way to the gascolator. Wrong!
Apparently fuel injected engines are not tolerant of anything other than 100% clean fuel. It was no fun having the always smooth running engine start stumbling in the downwind leg to land. Luckily the loss of power was near a runway.
I mentioned my engine issue to an old timer pilot that has forgotten more than I can ever hope to learn and his first comment was, 'did you sump the gascolator?'
There was a wee bit of water/gunk had accumulated. Thereafter, I would not be comfortable to fly without first checking the gascolator.
The RV3 I now fly is carbed and maybe more tolerant of contaminates in the fuel? Though I have to turn the boost pump on then get down on my backside flat out on the floor to access the gascolator, would not consider flying without checking the gascolator.
My 2 cents
rmarshall234
Well Known Member
Have you drained the float bowl of the carb lately? A good thing to do at each annual bc that's where the water and crud accumulate before they present themselves as a problem.
Same for me and my RV7. I remove the bowl and screen at each CI, as well as the carburetor's finger screen but have never found anything. I sump each tank before flight, which is where I occasionally have found debris and water.
Sump it..may save your bacon
I have one on my -4 per plans and Bingelis book recommendation when built in Jurassic era. I have a small hole in my lower cowl that I can sump through with a standard drain tool. A few years back I witnessed a return to field deadstick Glassair that was just pure luck...He had not owned it for long, and it sat on our ramp around Xmas time while he visited family and it rained a couple times. Had the whole family there for his departure home to Fla. Did a non eventful runup, took off and did high speed zoom climb at steep angle and at 500-800 feet, backfire pop and silent, managed the dreaded turnback but was so fast he had to force on runway , overshoot and destroyed the plane. We pulled the cowl and the hidden, inaccessible gascolator was full of water to the top. Im sure the zoom climb force fed water that was there for a while. Gave me a new respect for sumping mine. My -4 is always hangared,and in 12 years, I have never got a drop of water out of it, and yes, I have do it with the boost pump on.
I have one on my -4 per plans and Bingelis book recommendation when built in Jurassic era. I have a small hole in my lower cowl that I can sump through with a standard drain tool. A few years back I witnessed a return to field deadstick Glassair that was just pure luck...He had not owned it for long, and it sat on our ramp around Xmas time while he visited family and it rained a couple times. Had the whole family there for his departure home to Fla. Did a non eventful runup, took off and did high speed zoom climb at steep angle and at 500-800 feet, backfire pop and silent, managed the dreaded turnback but was so fast he had to force on runway , overshoot and destroyed the plane. We pulled the cowl and the hidden, inaccessible gascolator was full of water to the top. Im sure the zoom climb force fed water that was there for a while. Gave me a new respect for sumping mine. My -4 is always hangared,and in 12 years, I have never got a drop of water out of it, and yes, I have do it with the boost pump on.
pa38112
Well Known Member
I dont sump mine. I clean it every condition inspection and usually find a small amount of fine dirt, but never found any water.
If my plane were stored outside or was in a heavy rain,
I would probably sump it.
The only way water could get to the gascolator would be if it was pumped there by the fuel pump. Sumping the tanks should get any water before it gets picked up and pumped to the gascolator.
If my plane were stored outside or was in a heavy rain,
I would probably sump it.
The only way water could get to the gascolator would be if it was pumped there by the fuel pump. Sumping the tanks should get any water before it gets picked up and pumped to the gascolator.
To "sump" or not to "sump"; that is the question.....
It is part of my preflight to drain both wings and gascolator, both in the Cub (placarded to do so; lowest point in the fuel system is the gascolator) and in SuzieQ (fuel pump thumping). I have rarely found water in the tanks and more rarely found water in the gascolator. Usually debris/dirt. Water rarely found in tanks after a good Rain at OSH but I also usually cover the caps during a Rainstorm.
I tap the quick drains after EVERY fuel up as part of my miniature walk-around after fueling. Never know what you are pumping into your tanks. I have found water after refueling but usually crud. And have never left a tank cap off....
SO: tapping two tanks and a gascolator is part of my standard routine. I've done that since 1972 and don't see me changing after this many years.....
If I couldn't tap the gascolator, there would be a little part of me that would be uneasy...
What if...... If I had one that was not accessible, I would find a way to make it so. IMHO
It is part of my preflight to drain both wings and gascolator, both in the Cub (placarded to do so; lowest point in the fuel system is the gascolator) and in SuzieQ (fuel pump thumping). I have rarely found water in the tanks and more rarely found water in the gascolator. Usually debris/dirt. Water rarely found in tanks after a good Rain at OSH but I also usually cover the caps during a Rainstorm.
I tap the quick drains after EVERY fuel up as part of my miniature walk-around after fueling. Never know what you are pumping into your tanks. I have found water after refueling but usually crud. And have never left a tank cap off....
SO: tapping two tanks and a gascolator is part of my standard routine. I've done that since 1972 and don't see me changing after this many years.....
If I couldn't tap the gascolator, there would be a little part of me that would be uneasy... What if...... If I had one that was not accessible, I would find a way to make it so. IMHOYou need to be sure the engine will not quit during flight.
If you never had gunk in the filters during 50 hr inspections and it´s parked in a heated locked hangar and regularly flown, there will be no water in the fuel.
If parked outdoors there is a real risk that rainwater enters the tanks regardles
what fuel caps you have. If left outdoors over night with other than full tanks, there is a real risk of condensation especially when close to a lake or coast.
If parked at an unattended airport, you don´t know what happens.
If flown by someone else, you don´t know.
So I would say it depends.
If you never had gunk in the filters during 50 hr inspections and it´s parked in a heated locked hangar and regularly flown, there will be no water in the fuel.
If parked outdoors there is a real risk that rainwater enters the tanks regardles
what fuel caps you have. If left outdoors over night with other than full tanks, there is a real risk of condensation especially when close to a lake or coast.
If parked at an unattended airport, you don´t know what happens.
If flown by someone else, you don´t know.
So I would say it depends.
I haven’t found anything in my fuel samples either - tanks or gascolator, but I still do it. On my firewall mounted gascolator, located per my build plans, I made an extension out of a brass nipple from Home Depot with an adapter and the quick drain that ends up flush with a hole in the bottom of my cowl for sumping. I can turn on my boost pump for a squirt, or turn on my boost pump and close the fuel selector valve to capture some pressure. Then run around to the front and get a descent squirt of fuel for the test. Don’t forget to open your fuel selector valve after if you do it this way……. You won’t get very far if you don’t. I just cleaned my Andair gascolator today doing my CI. I found a small ball of what looks like lint about half the size of a pencil eraser, so the gascolator did it’s job. That kind of stuff won’t show up in your samples because it gets stuck in the filter, but water and heavier dirt particles will.
Gascolator cooling.........
....which is why I have mine enclosed with a cooling air duct blasting cool air on it....
....which is why I have mine enclosed with a cooling air duct blasting cool air on it....
I can't think of any model RV, that Van's designed their fuel valve below the wing sumps of the aircraft....
Therefore the lowest location of the fuel system is in the fuel tanks at the drain petcock.
The RV15 will be the first RV model that will benefit by having a gascolater installed and inspected before each flight.
Van's head of design for over 16 years, that brought us the RV 7, 8, 9, 10, 12, and 14, did not install a gascolater on his own RV6....... go figure.
Therefore the lowest location of the fuel system is in the fuel tanks at the drain petcock.
The RV15 will be the first RV model that will benefit by having a gascolater installed and inspected before each flight.
Van's head of design for over 16 years, that brought us the RV 7, 8, 9, 10, 12, and 14, did not install a gascolater on his own RV6....... go figure.
I may have missed it but the electric boost pump must be on to get anything out of the gascolator on my airplane. Sumping the gascolator without the boost pump on, I get NOTHING out of my gascolator.
The first year of flying, I sumped the gascolator before 1st flight every day. On the RV-6, the wing tank sump is the lowest point in the fuel system. After lots of checking the first year and the only time I have ever seen any water was after flying through rain. My SOP has been to only sump the gascolator after flying through rain or any event that the airplane has been exposed to water.
Not saying others should do as I do as it is better to test and not need than to overlook a possible problem. I do not suggest skipping the sump of the gascolator till you are 100% certain that water does not get that far in your fuel system.
The first year of flying, I sumped the gascolator before 1st flight every day. On the RV-6, the wing tank sump is the lowest point in the fuel system. After lots of checking the first year and the only time I have ever seen any water was after flying through rain. My SOP has been to only sump the gascolator after flying through rain or any event that the airplane has been exposed to water.
Not saying others should do as I do as it is better to test and not need than to overlook a possible problem. I do not suggest skipping the sump of the gascolator till you are 100% certain that water does not get that far in your fuel system.
I can envision an extremely unlikely scenario where a few drops of water get pumped through the fuel system and happily get shoved through the combustion chambers without issue, but on shutdown, whatever is in the gascolator settles to the bottom.
A few drops here, a few drops there...after a few months of that a guy could have a nice slug of water sloshing around in there.
I'm not putting a gascolator on my airplane, but if I had one, I would definitely be sumping it
A few drops here, a few drops there...after a few months of that a guy could have a nice slug of water sloshing around in there.
I'm not putting a gascolator on my airplane, but if I had one, I would definitely be sumping it
Quite a few of those designs have had gascolators installed in the company airplanes, so I am not sure what you are saying……….
A gascator doesn’t have to be located at the low point in a fuel system to be effective. It is an artificial low point in the system, that used properly, can be an effective filtering system.
My current airplane has a gascolator. Do I sump it? Not during every preflight but I do pretty regularly.
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Thanks Scott for your statement. I was going to ask why does everyone state the gascolator has to be at the lowest point. If the gascolator is designed to separate water and debris, what does it matter where the gascolator is mounted? The gascolator can be mounted on top of the cowling and it still should work the same if it were mounted on the gear leg. And if you have an inline filter the only real need for a gascolator is to catch water. And for FI, don’t all fuel servos have a finger strainer/filter? So if you don’t have a gascolator on a FI engine as long as you shake the wings before pre-flight to get any water in the wings to the lowest point and sump it you shouldn’t need a gascolator. And according to DanH, small amounts of water are not a problem for FI unlike for carbs where water can collect in the bowl.
And like someone mentioned in an earlier post, make sure you clean the carburetor bowl annually.
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Scott, I do agree that a gascolator can provide a low spot in the fuel system. What I am saying is that it is not the lowest spot in the fuel system. That location remains as where Van's placed the tank sump.
In order for water to make it to the gascolator, you would have to pump it there. I can only think of two ways water can get into the gascolator.
1. You fly through rain and your fuel cap seals are so bad that more than 8oz (RV6 tank) leaks in and is picked up by the pump and delivered to the gascolator by first lifting it to the gas valve that is over 5 inches (guess!) above the fuel pick-up.
2. During your walkaround, you reach in and turn on the master, lower the flaps and flip on the fuel pump to go sump the gascolator. As you take your sample, the pump just sucked up any water that was in reach of the pick-up. That water will not make it to the gascolator during your sample, but will be there the next time you sample...... Sump Your Tanks First.
Should you install a gascolator on your RV....... YES. Do you need one? It all depends on what you do with your airplane. Is it the lowest point in the fuel system?.... NO. Will it trap water?.. YES, only if you fail to sump your tanks properly. Will it save your life if you are flying in a rain storm without fuel caps? YES, but only for about 5 more minutes......
In order for water to make it to the gascolator, you would have to pump it there. I can only think of two ways water can get into the gascolator.
1. You fly through rain and your fuel cap seals are so bad that more than 8oz (RV6 tank) leaks in and is picked up by the pump and delivered to the gascolator by first lifting it to the gas valve that is over 5 inches (guess!) above the fuel pick-up.
2. During your walkaround, you reach in and turn on the master, lower the flaps and flip on the fuel pump to go sump the gascolator. As you take your sample, the pump just sucked up any water that was in reach of the pick-up. That water will not make it to the gascolator during your sample, but will be there the next time you sample...... Sump Your Tanks First.
Should you install a gascolator on your RV....... YES. Do you need one? It all depends on what you do with your airplane. Is it the lowest point in the fuel system?.... NO. Will it trap water?.. YES, only if you fail to sump your tanks properly. Will it save your life if you are flying in a rain storm without fuel caps? YES, but only for about 5 more minutes......
The mesh screen in the gascolator that Vans supplied is finer than the mesh on the fuel tank pickup tubes, so it will help to trap any particles that may get through, in addition to any water that hasn't been drained from the tanks before it was picked up and pumped through.
Unless the tail is raised, ie. on an A model or a tailwheel model in flight. At that point, a gascolator (if properly installed) does become the lowest point in the system. Once the water is trapped there, it won't get out until you sump it.
I have found water in my gascolator. RV-6, and hangared as long as i've owned it. I sump before flight.
Does the gascolator need to be mounted at the lowest point?
I keep hearing the only way to suck water into the gascollator is by using a fuel pump which must be insinuating an electric fuel pump since all aircraft engines have a mechanical fuel pump. If the engine driven fuel pump is drawing fuel from the tanks it will also draw water as well. So what makes an electric fuel pump any more efficient to pull water into the fuel system than the engine driven fuel pump? The electric fuel pump is a back up in case the mechanical fuel pump fails.
I can’t imagine anyone not having an in-line fuel filter at the very least which has way more filter area than a gascolator to filter out way more debris. And we certainly aren’t considering the fuel pick up screen which is nothing more than filtering out large debris.
Again why does everyone keep stating the gascolator needs to be at the lowest point of the fuel system when the fuel is being filtered by the gascollator, and as stated by Scott, the gascolator provides an artificial low point in the system, thus separating the water (and debris for those of you who do not have an in-line filter) from the fuel??? Mechanically it shouldn’t matter where it’s mounted on the firewall. If you can come up with a logical explanation as to why the gascolator needs to be at the lowest point, I’d like to hear it.
This reminds me of a story I heard a long time ago. The mom tells her daughter when she cooks the ham to cut off the ends before putting it into the oven because it will make it taste better. The daughter asked why. The mom responses, because that’s what my mom did when she cooked the ham and it tasted so good. So the daughter tells her mom, let’s call grandma and ask her why cutting off the ends of the ham makes it taste better. So they call grandma and ask her. Grandma says, because back then we had really small ovens and the ham would not fit into the oven without cutting off the ends. Hmmmm, I think grandpa Scott is right.
I keep hearing the only way to suck water into the gascollator is by using a fuel pump which must be insinuating an electric fuel pump since all aircraft engines have a mechanical fuel pump. If the engine driven fuel pump is drawing fuel from the tanks it will also draw water as well. So what makes an electric fuel pump any more efficient to pull water into the fuel system than the engine driven fuel pump? The electric fuel pump is a back up in case the mechanical fuel pump fails.
I can’t imagine anyone not having an in-line fuel filter at the very least which has way more filter area than a gascolator to filter out way more debris. And we certainly aren’t considering the fuel pick up screen which is nothing more than filtering out large debris.
Again why does everyone keep stating the gascolator needs to be at the lowest point of the fuel system when the fuel is being filtered by the gascollator, and as stated by Scott, the gascolator provides an artificial low point in the system, thus separating the water (and debris for those of you who do not have an in-line filter) from the fuel??? Mechanically it shouldn’t matter where it’s mounted on the firewall. If you can come up with a logical explanation as to why the gascolator needs to be at the lowest point, I’d like to hear it.
This reminds me of a story I heard a long time ago. The mom tells her daughter when she cooks the ham to cut off the ends before putting it into the oven because it will make it taste better. The daughter asked why. The mom responses, because that’s what my mom did when she cooked the ham and it tasted so good. So the daughter tells her mom, let’s call grandma and ask her why cutting off the ends of the ham makes it taste better. So they call grandma and ask her. Grandma says, because back then we had really small ovens and the ham would not fit into the oven without cutting off the ends. Hmmmm, I think grandpa Scott is right.
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There have been more than 1 or 2 Piper Aztecs (IO 540 x2 ) and other FI twins and single engine AC fail to stay in the air when small amounts of water in the fuel form ice crystals which restrict flow by progressively blocking fine mesh filters and even finger strainers at the servo body inlet. At altitudes (and latitudes) where air temps are below freezing for long enough ice crystals are bad news. Water contamination in any fuel system is to be prevented as much as possible and eliminated by all means available.
[email protected]
Well Known Member
I don’t have a gasalator on my RV10. I have an Airflow Performance FM300 throttle body and the Airflow Performance electric fuel pump with the huge corrugated screen just prior to the fuel pump. I sump my tanks every time and have never found any water, not even a drop when the aircraft has been in heavy rain outside on a road trip. I keep the tanks full almost all the time, and the aircraft is hangered at HND in the desert when I am home. 400+ hours since finished in 2020. I make sure the fuel caps are adjusted to be snug and I will replace the O rings if I find the slightest imperfection. Condensation is a big problem in the midwest and southeast, which is why I always refuel as soon as I land. No air in the tanks, no condensation.
A friend of mine put a gasalator in his RV6 with a very fine ceramic filter. The lead in the gas plugged it up.
A friend of mine put a gasalator in his RV6 with a very fine ceramic filter. The lead in the gas plugged it up.
Lead in a flilter....
It would be a little difficult to get ALL the air out of a tank. Even a little air can cause the water to condense out. Great to hear you have not had a problem.
Huh. Interesting. That would be removing the lead on a molecular level. THAT would be a very fine filter! How did they determine it was lead that was the problem? Curious minds want to know.....
It would be a little difficult to get ALL the air out of a tank. Even a little air can cause the water to condense out. Great to hear you have not had a problem.
Huh. Interesting. That would be removing the lead on a molecular level. THAT would be a very fine filter! How did they determine it was lead that was the problem? Curious minds want to know.....
This may just be a misinterpretation. On the ground before flight you can't sump a gascolator on a TW RV because there's no pressure in the system to push out a sample. You might get a few dribbles but that's it. So you have to turn on the electric pump to pressurize the system. Sump the tank first, to be sure there's no water in it, and then sump the gascolator, to get any water that may have been brought there on a previous flight (and you're right, that could be from either the electric or the engine-driven pump).
A gascolator can hold a lot more debris in the bottom than a filter can in its folds, and not restrict the flow in the process. A filter will ultimately become a plug once it's picked up enough debris, and cleaning it requires disconnecting your fuel lines and trying not to spill fuel everywhere. A gascolator is designed to be cleaned easily.
Thanks for all your replies. A little more confused than I was before I posted this and I’m guessing the non sumpers are under represented so they’re not shamed. I’m going to work on a way to make sumping mine a practical part of my pre flight, but still curious as to why there’s disagreement about the low point in the system. Also, why’s the gascolator included in plans without the corresponding infrastructure to make it a practical part of the pre flight?
I periodically fly a 172M. It has a pull-knob just inside the oil door...when you pull it, it expels a stream of gasoline onto the ground thereby "sumping" the gascolator. It's a routine part of the preflight.
I was surprised to hear that Van's doesn't call for an accessible gascolator with drain. My -9A has one at the lowest point and I thought that they all did. I'm sure that they have a rationale...I just don't know what it is.
gmcjetpilot
Well Known Member
The Gascolator is also for filtering, straining particles. sediment as well as a water separator. It is suppose to be the lowest point, but regardless it will catch water at some point. The gascolator is it's own low point. Once the fuel is flowing it will go through the gascolator regardless of location it still filters particles out and separates water out, if any water got that far. The gascolator is a "how goes it" from the last flight.
The logic of draining tank first and foremost is sound, and if no water found no water should be in the down stream fuel system. However it still does not clean out anything the Gascolator that may have collected from the last flight, including a little water and any dirt, sediment if you don't drain it.
Where does water come from? It comes from the fuel tank. Hew does water get in tank? Heavy rain and leaky gas gap? Biggest fear is refueling and getting a big slug of water from the fuel truck or underground fuel tanks.
As pointed out some planes have preflight procedures that does not require you to collect a gascolator sample, but you do pull a cable to spit gas out the gascolator bowl onto the ramp. This clears the bowl of stuff. RV builders could so something similar. I get crawling on the ground with a sample cup is no fun. We all have drained fuel from tanks and "gascolators" for decades and rarely if ever found water. So we might get complacent.
There are massive threads about fuel system design. One topic is to install a gascolator or not. Some builders substitute in-line filter or filters that are not drainable, unless you break the fuel line and remove them. The nice part of a gascolator is you can drain it and remove the bowl for inspection easily without breaking the fuel line. Pulling the bowl every other oil check and condition inspection is a good idea. It is a fuel filter. There is a lot of freedom in building but somethings should be kept standard and as simple as possible.
The logic of draining tank first and foremost is sound, and if no water found no water should be in the down stream fuel system. However it still does not clean out anything the Gascolator that may have collected from the last flight, including a little water and any dirt, sediment if you don't drain it.
Where does water come from? It comes from the fuel tank. Hew does water get in tank? Heavy rain and leaky gas gap? Biggest fear is refueling and getting a big slug of water from the fuel truck or underground fuel tanks.
As pointed out some planes have preflight procedures that does not require you to collect a gascolator sample, but you do pull a cable to spit gas out the gascolator bowl onto the ramp. This clears the bowl of stuff. RV builders could so something similar. I get crawling on the ground with a sample cup is no fun. We all have drained fuel from tanks and "gascolators" for decades and rarely if ever found water. So we might get complacent.
There are massive threads about fuel system design. One topic is to install a gascolator or not. Some builders substitute in-line filter or filters that are not drainable, unless you break the fuel line and remove them. The nice part of a gascolator is you can drain it and remove the bowl for inspection easily without breaking the fuel line. Pulling the bowl every other oil check and condition inspection is a good idea. It is a fuel filter. There is a lot of freedom in building but somethings should be kept standard and as simple as possible.
Take a tape measure or laser measure and measure from the ground to the wing tank skin at the petcock drain. Then, try to find a lower spot in the fuel system.
It's not that you're looking for a lower spot. It's that you're looking for a low spot in the system that can trap water that you can't remove until it moves to a spot with a drain in it.
When I was re-determining empty weight, re-calibrating the tank gauges, and changing tank/gascolator drains, I drained the tanks completely...it then still drained a lot of fuel from the gascolator when I removed that drain. Boost pump not required.
