pipe compound

Tapered pipe threads are the only threads where tape or paste should be used. If the automotive aftermarket quit using tapered NPT completely, mine would be tears a joy.

It's not so much that teflon tape disintegrates or partly dissolves in fuel, it doesn't, it's that little tiny pieces of it break off and plug small holes in whatever is downstream. Like in carb emulsion tubes, BT,DT.

The "one thread back" rule is a good one if you want to use tape. I prefer PST or a similar teflon bearing paste on low dollar, low importance systems. Doesn't take much and I can wipe off the excess right after assembly. If the system is one where a leak could cause death or major damage I use Lock-tite 545, but be forewarned that it is not inexpensive!