I was wondering why some hot water heater repair guides said to use Teflon
tape (TPFE?) on the water lines but pipe dope (TPE?) on the gas lines yet
the tube that I bought says it works for both gas and water. That's
confusing. I was careful to only state in my hot water heater step by step
guide just what I had read in other guides, taking the best except where
they conflicted.



It's mostly a matter of preference. When using teflon tape, there's yellow
stuff rated for fuel use which is what you should use on gas lines, or you
can use pipe dope. A book I have on plumbing which is written by a long time
plumber recommends using both, and indeed I've started doing that on gas
lines and have yet to have a leak. Put on a thin coat of pipe dope, wrap a
couple layers of teflon tape tightly, then brush a little pipe dope over
that and screw it in. Make sure the tape stays on the threads and doesn't
scrunch back when you thread it in, and screw it down tight enough but not
too tight, I know that's probably not very helpful but I don't know how to
describe it. Use a pipe wrench, they're cheap. I use a pair of vice grip
pliars to hold the existing pipe so I don't unscrew it while unscrewing
fittings from that.