Should I apply 3 or 5 winds of Teflon tape around the threads of the union on the p-trap?
Do the threads of the trap adapters require tape too?

No and No. Those joints are made by compression via. a compression washer or the molded tapered end of the J-tube portion of the p-trap assembly.

no tape on either. i lubricate the trap union with a dab of plumbers grease just to make it slipperier. (there's that word no one can spell)

Thanks KC and packy ...



Edited 1 times.

More slippery.

NO

if metal trap use a dab of plumber's grease

if plastic, nothing

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

The seal is by means of the slip washer, so I NEVER use any lubricant. If a slip nut had a "tight thread", which they do not, then it might have some value.

I believe the ? was about the swivel union OF the trap itself

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Whatever, the answer is the same. Very few traps have ground joint swivel connections. I haven't seen one for many decades.

quote.. "Very few traps have ground joint swivel connections"
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this is the only kind we are allowed to use. the trap that uses a beveled washer to make the taper for a swivel joint is illegal in massachusetts.

Must be because it causes cancer or is less expensive to install.