Finally redoing the 1/2 bath, just a sink and toilet. The toilet waste goes straight down about 18" before it turns to head toward the main. This bath is on the main floor and in an addition, so it doesn't tie into the main stack serving the 2 upstairs baths.

Sink is vented by an AAV, and I plan on tying the sink drain into the toilet with a 3x3x1-1/2 wye. Question is should the wye be on the vertical section of the toilet drain directly under the toilet, or should I tie into the horizontal section after it turns? Does it make a difference?

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Not a plumber by trade but a fierce DIYer

it makes no difference.
if on the vertical use a sanitary tee.
I would use 2 inch pipe because you are actually wet venting the toilet thru the lav drain.
to be clear. 3 x 3 x 2 san tee in the vertical toilet drain.
put a 2 inch cleanout tee in the lav drain.

Got it, thanks. Could I use a wye to tie into the vertical or it has to be a san tee?

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Not a plumber by trade but a fierce DIYer

only fitting that would be prohibited on the vertical would be a straight tee. (no sweep to the branch).
I only suggest a san tee because it is cheaper than a "Y" and street 45.
but, if you are really " John Beresford Tipton ", use what ever you want. hahaha..

Boy! Packy I haven't heard that name for a long time.

OK, had to Google that name....I've heard of the show but it went off the air the year I was born....

Anyway I already bought the wye, but I can take it back and get a san tee...

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Not a plumber by trade but a fierce DIYer

deleted

duh

brain-freeze

duh

(thanx for the pick-up, Sum)

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



Edited 1 times.

It doesn't sound like a trap arm tie in though. From his description I assume his trap arm is higher say 12", 14" off the floor so I assume this is after the tie in the drain/vent runs vertically down to below the floor and where it has to tie into the big drains from the toilet, where he has a choice of tying into the vertical section of the toilet before it goes horizontal or tie it in further downstream into the horizontal section.

Personally I would tie it in at the horizontal section further downstream with a WYE as he is wet venting the toilet via his AAV at the sink. In addition if he ever needs another fixture like a shower or bidet he can tie into the 2" if necessary.