I installed a new gas tank today in my 52 Chevy (the old one had a hole in it). I can't stop it from leaking around the pipe nipple I screwed into the bottom of the tank. I used teflon tape. When I got the tank, it had a temporary bolt screwed into that hole, and the threads don't quite match my pipe nipple. I used a pipe nipple because that's what was on my old tank. It seemed to thread into the hole just fine, but it never really gets tight enough to be gas-tight. In fact, I could screw the whole thing right into the tank.

What kind of a fitting should I be using? Is teflon tape not the best thing to use?

My dad always told me, "Don't force it, get a bigger hammer".