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Discussion Starter · #1 ·
I'm having my basement slab jackhammered up and a new one poured, and they will be roughing in plumbing for a full bathroom (tub, toilet, sink), and a laundry drain.

I've been able to find lots of information on a primer for the floor drain primer, and will have them run a 1/2" line to the floor drain for that purpose.

However, I'm having a hard time finding information on a drain primer for the tub p-drain.

My expectation is that the contractor will give me a 12" x 12" box where the tub trap will reside.

Since the tub trap won't be poured permanently in place, should I run a 1/2" pvc line for it, then transition to a flexible plastic line?

Any advice would be appreciated, plus any sources for plastic p-traps with primer nipples.


Premium Member
12,184 Posts
Typically, tubs don't have primers installed, but if you don't use it often it may not be a bad idea.
I use "bap adapters" on floor drains- not sure if they come in 1.5" They're glue couplings with an 1/2" fitting tapped into the side. Install it above the p trap. To prime the trap, I'd run 1/2" pex from the lav to the tub- in the wall, not the floor.
If you use a slip joint waste and overflow, perhaps use a DW or condensate tailpiece instead of the bap adapter.
Primers can also be supplied from a toilet too. The trap is primed when the toilet is flushed
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