Boat Fuel Tank - Pressure Testing

What I did to test a 100 gallon tanks was set it off the ground about a foot. Fill it with water, then I used a piece of PVC piping that was 16' long and 2" wide, connected that to the fill and having it standing straight up and filled that with water. Been a long time, but if I remember right, a gas tank needs to be tested up to 6 psi. By going up that height with the pipe, that gave the tank a 8 psi head pressure.

Another way, fill the tank with water. Block off the fill. Hook up a line with a gauge and a air valve and hook up a compressor with a shut off valve. Bring the pressure up to 8 psi, close the valve and let it sit for a few hours.

By all means, this is NOT CG approve. But for you to feel safe, it will work. Also, if using a compressor, DO NOT go OVER 8 PSI.

Drain the tank of the water and add about a 1/2 gallon of Denature Alcohol when you fill it with gas. Also keep eye, drain any fuel filters as needed.

I put an air compressor to my aluminum, took it up to 4psi, then covered the tank in soapy water, no bubbles, hasn't leaked

That's good. Filling it any more is really pointless for checking leaks and will likely damage the tank, especially if it's 1/8" thick or less.

It's much safer to do a hydrostatic test with a head tube than filling with air. If you over pressurize a pneumatic test, a rupture will be much more violent.