Valve question

[Shane]

Because Teflon tape is NOT a sealant ... it's a lubricant.

http://en.wikipedia.org/wiki/Thread_seal_tape

Thread tape is appropriate for use on tapered threads, where it is the thread itself that provides the seal surface ... <snip> ... the defining characteristics of PTFE is how good it is at defeating friction. The use of PTFE tape in tapered pipe threads performs a lubricating function, which more easily allows the threads to be screwed together, to the point of deformation, which is what creates the majority, if not all, of the seal.

I can promise you that the natural gas feed line in MY house does NOT have Teflon tape on it. I can not speak for others.