I also did a pressure test and squirted soapy water and found no leaks until they where mounted on my plane and full of fuel. My recommendation in testing the tank is to put a 1/2- 1 gallon of fuel in them and lay them on the floor rear baffle side down. If they are going to leak, it will be a high percentage chance coming from the rear baffle area. If you see stains on the floor you will know. Also, I used the thinner viscosity proseal to repair leaks. It will flow better into small areas.
Al Girard, Newport, RI