soldering 1/4 return line

[72bluNblu]

Yeah it wasn't really hard per se, but it did take a few tries to get the technique down...

[kslush]

Vacuum caps won't work, the fuel will eat the rubber if you ever fill the tank above the level of the sending unit.

There are caps of different grades of rubber that will survive in this application.  Also, gasoline vapor eats up materials much faster than liquid gasoline.