Do your self a favor. Put a half gallon/gallon of av gas in the tanks and let the tank rest horizontally with the rear baffle downward. Put it on the garage floor.
If you have a leak it will most likely come from the rear baffle area. You will see spots on the concrete if it leaks. I pressure tested mine with soap and there was no sign of bubbles. Yet both of my tanks had small leaks discovered when mounted on the plane. I would have saved a lot of time if I put fuel in the tanks when they where not mounted to the wings. The true test.
Al Girard, Newport, RI