Guys I think he is talking about the PIPE THREADS into the tank. Use Teflon paste. Teflon paste is a lubricant and not a sealant for tightening and releasing. Wipe it clean if you are doing a 100 PT. car. Pipe threads are tapered and should seal themselves. AMEN
If this is a stock 40 Ford gas tank the only pipe threads on this tank are the drain plug threads.
The filler pipe is not a pipe thread. The fuel line is not a pipe thread. It is sealed with a compression ferrule.
So the only place to use sealer is on the drain plug.
Bill