I used a length of vinyl tube to set up a manometer for leak testing the tanks.
I had purchased a test kit from Van’s (not realizing they would also send a test kit with the wings) but I ended up needing both as I also needed to cap the return fuel line.
I found some wide packing tape that allowed me to seal the fuel caps with a single strip of tape. This worked well and I had no leaks at the caps.
I calculated the head required for 1 psi and pressurized the tank. My garage temperature is constant so the only other variable was air pressure. The water level went up and down the expected amount with the reported pressure at KMSO.
I also used a spray bottle with soapy water to also inspect for leaks.
Both tanks held pressure for 48 hours and didn’t show any signs of leaks.