The Stovebolt Site Forums The Shop Area General Truck Talk Fuel leak at tank

There is a difference between NPT (National Pipe Thread) and NPTF (National Pipe Thread Fuel). Only the latter type is designed to seal without teflon tape or pipe dope. NPTF threads rely on an interference fit (metal-to-metal crush) where crests and roots deform into each other without sealant.Unfortunately it's nearly impossible to tell the difference between them. So definitely use pipe dope (Gasoilia is a recommended brand.) It's been rumored that some reproduction tanks had straight threads rather than tapered threads and are nearly impossible to get sealed. If that's the problem with your tank, you MIGHT be able to run an NPT tap thru it and get a little taper in the threads. You'd still need to use pipe dope to get it to seal.