[David Bienvenu]

I own an industrial radiator and heat exchanger shop. Pressure testing is something we do every day. We hydrotest to 750 PSI.

Be very careful pressure testing a tank with air. Depending on the construction materials of the tank and the size it may not be safe to go above 5-10 psi. PSI is pounds per square inch. The more surface area a tank has the more pressure applied to the walls. We would consider it dangerous to put 25 PSI of air in an empty square or rectangular 1/8" aluminum welded tank. Filled with water and using a hand operated pump (Like plumbers use)you can go higher. The fact is that water won't compress and if the tank splits open worst that will happen is you get wet.

As shared above, 5 psi air and a spray bottle of dish washing soap and water will do the trick. (409, windex etc. won't "hang in there")However remember that if the tank is not empty you will only find air leaks above the fuel level line.