Might check this out... but I think fuel lube is a thread sealant. It works for a while then makes it worse on o rings. Some use DOW 4 or similar lube. There is a very toxic lube that is used for carb rebuilds that stays slippery in contact with fuel. Expensive. I cover the caps when prolonged rain is expected and I am parked out. Got a blob of rainwater in January that did not show up until 4th flight, even though I sumped before each. It forced a landing... and subsequent hot brakes etc. (not much runway left when it faltered on takeoff)
I sump a large quantity now, into a clear jar. If clean, I put it back in the tanks.
I also am not a fan of running the electric pump in order to get a sample from the gascolator. It pumps so hard that I suspect turbulence would mix the water and fuel temporarily. Just a theory. I prefer to let it run out slowly, as gravity and venting allow. Seems like any water at the bottom of the gascolator would have a greater chance of getting out and being seen in the sample.
Any contrary ideas, theories or practices welcome in a heart beat.