For compression connections, don't use anything. That would include supply lines for sinks, toilets, etc and also slip-joint connections on drains.

As for threads on shower head, shower arm, etc, you can use either. One other place to use it (either) is when you're putting together the parts for a sink drain (other than the trap and any slip fittings). If it's PVC, make sure the thread compound say it's ok with it.

Not to hijack...but related question:

For 3/4 copper female to PVC male: teflon or pipe compound or? If teflon, approx how many wraps?

Personally copper male to PVC female has always been the better transition.
Usually 3-4 wraps, and try. If to loose, back out and do over with more

While we all commonly call it Teflon tape, technically the word "Teflon" is a registered trade name, which may only be used by the Dupont Chemical Corp. All other manufacturers should label their product as "PTFE (Polytetraflouroethylene) Pipe Thread Tape" Please note very carefully that is says "Pipe Thread Tape". PTFE Tape and "Pipe Joint Compounds" are to be used only on NPT (National Pipe Taper) male threads. Neither PTFE nor Pipe Joint Compound are to ever be used on SAE mechanical threads or as a gasket sealer such as for the sink basket gasket as was suggested above and absolutely nothing is to be applied to the threads on the PVC slip type DWV fittings such as P-traps, tailpieces, Waste & Overflow Kits, End Waste kits or Center Waste kits.

When PTFE tape was first introduced into the plumbing industry all they made was the thin " wide "single density" tape such as we find on the small blue & white or red & white $.98 cent plastic spools in the hardware stores. Shortly thereafter they began making ¾" & 1" wide rolls, which were principally marketed through the Plumbing & HVAC supply houses. In the early 80Âs they began making a "Double Density" PTFE tape which was twice as thick as the single density tape, however, here again it was primarily only marketed direct to the Plumbing & HVAC industry through the trade supply houses.

Shortly after the double density tape was introduced the National Gas Code was amended prohibiting the use of single density PTFE and requiring the use of pipe dope or double density PTFE tape on gas lines. Needless to say, even though the Double Density PTFE tape was approved for water service nonetheless it was soon referred to as "Gas Tape".

The ASTM (American Society of Testing & Materials) has now amended the standards for PTFE requiring 3 layers of "Triple Density" PTFE tape to seal threads on pipe from 1/2" to 2" in diameter.

In addition, they have now adopted a color-coding system to define the different types of PTFE tape.

White Â--Single Density for use on pipe threads up to 3/8" diameter
Yellow---Double Density- Gas Pipe
Red---Triple Density for use on pipe threads from ½" through 2"
Green----Certified Oil Free- for use on Oxygen and Medical gas lines.
Copper---Contains copper granules- May be used as a mechanical thread lubricant but not a sealant.

I prefer to use pipe dope on all threads that are intended as a permanent joint or threads that will ultimately be in a concealed location and I use PTFE on joints which we can expect will be changed periodically such as shower arms, shower heads and angle stop valves that have a threaded input port.

Now in regards to the Copper x PVC connection

Quote; "Personally copper male to PVC female has always been the better transition."

There is only one minor problem with that idea. The plumbing Codes expressly prohibit any Female threaded PVC fittings.

"No female threaded PVC fittings"
Ref; IRC-2904.16.2 & UPC-606.2.2

Depending on how you wish to interpret the code, most cleanouts would be prohibited, along with some valves, meter connections and many other install items.
There are alot of minor problems with most codes yet they are needed unless we wish to step back 100+ years or move to Mexico.

The Plumbing codes are like the Holy Bible, they are both only difficult to understand when people try to make it say what they want it to say, rather than accept what it actually says.

Interesting comparison, depending on what book you read in the bible, Jesus was different to many.

Is "red" the same as "pink" which is sold in Home Depot?

It is called RED, but you are correct, the tape has more of a pink appearance..if in doubt check the label, it will say "Triple Density".

I guess I'll add my two cents worth as well.

I'm a gasfitter only, no plumbing. When I thread brass to brass I use dope only and prefer Rectorseal. When I thread black to black or black to brass I use about three wraps of single density tape and pipe dope. When I thread anything black for use in liquid piping I use dope, then tape, then dope. I personally have found these methods to be leak proof.

ASTM specifications prohibit using both dope and tape on the same joint.

Dope, tape and then dope
Thats a new one for me I've never heard

try sealing a 3" LP liquid pump line with just dope one time and you'll see why.

Thats true LP, but maybe they should prohibit these overseas black iron fittings too, some of them are almost egg shaped it seems.

A 3"Lp line shouldn't present much problems.

I have used the hardening type of Rectorseal on 6" saturated live steam lines firing at 1000psi (boiling temp 546degF)

Works well, just very messy!

well, Ive never tried that, but I know the dope/tape/dope method is foolproof and will keep that liquid lp gas inside those pipes for many many years.

Some complain that dope is too messy while others complain that they cannot get a good seal with it. That is true, but don't blame the dope.

If its too messy your applying to much dope and if you not getting a good seal you simply are not tightening the joint enough. When an NPT joint is properly tightened you should not be able to see more than 1 turn of thread on the pipe.

If you see more than one turn of threads exposed at the joint, get a bigger pipe wrench and torque it down.

For the 3" pipe mentioned above I always resort to my trusty old "Rigid" 60 aluminum pipe wrench.