In article .com, "Ken" wrote:

I think the basic principle to follow is that when the threads form the
watertight seal, then use teflon tape (e.g. NPT fitting). If the
threads are just there to hold a fastener and something else forms the
watertight seal, then no tape is necessary (e.g. compression fitting
with a ferrule).

You're missing the other purpose of using tape or dope: ease of disassembly.

--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?