We're adding a full basement bathroom (under a permit) and the framing and pluming are all roughed in. We hired a plumber.

The toilet has about 8 feet of waste pipe under the slab, tying back into the kitchen/laundry waste and then goes about 15 to a vent stack (existing) that exits the foundation above grade.

The shower has a 1.5" vent that sizes up to 2" right after the sink ties in and then that goes horizontally about 15 feet to where it ties into the main vent stack (existing) for two main floor baths.

We didn't exercise our option to add a slop sink in the basement outside one of the bathroom framed walls when the plumber was here and now it's involved to get him back, so I want to do it myself.

I can use some guidance in getting it right and to code.

I want to cut into the vertical 2" vent pipe coming from the bathroom sink, right before it T's into the horizontal vent run going to the main stack. I would use a sanitary T and then have about 3 feet of horizontal, 90 deg. elbow, and then drop to the sink stub.




For the drain, I need to follow a similar path parallel to the horizontal vent, turning the corner and stubbing out.



Is the sanitary T (as shown) the right connection?

At what point do I downsize to 1.5"?

How do I tie into that short vertical of the drain going into the concrete since it's locked in the stud?

Thanks guys!



Edited 4 times.

i am somewhat confused by your description of the plumbing layout.
if the shower drain is under the slab then it can not have a 1 1/2 inch vent as 2 inch is the minimum size allowed below grade.
you say nothing of the toilet vent ??

You can use two shielded couplings to get a tee into that short section of piping. I'd use a 2" X 2" X 1 1/2" tee there and use 1 1/2" piping for everything else. Had the plumber known about the sink in time, he could have used a back to back fixture fitting and vented both sinks with one vertical vent.

@Packy




Under the slab it's 2" and then downsizes to 1.5" Allowed?

The toilet has about 8 feet of waste pipe under the slab, tying back into the kitchen/laundry waste and then goes about 15 to a vent stack (existing) that exits the foundation above grade.

@North Carolina Plumber (NC)

I think the inspector is going to have a problem with the couplings. Is there a way w/o using those couplings and going all PVC?



Edited 2 times.

Going to 1 1/2" above the slab is fine. If you want to stay all PVC then you can glue slip couplings on both side of the tee, or you could cut the horizontal pipe and use a coupling there. You could cut the stud loose and let it pivot while you glue a tee in that vertical pipe, or you could cut a little notch in the stud,just above the drilled hole,so that the pipe could rise up enough to get the tee in.

Thanks North Carolina Plumber (NC) - great suggestions. Pivoting the stud is an interesting idea.

So where I cut-in the vent into the 2" vertical, that needs to be a sanitary T in the direction I've shown, correct? Then I can immediately size down to 1-1/2" for the rest of the leg and just slope 1/8"/foot down for the horizontal and turn 90 deg. down to the drain?

For the drain, 2" Sanitary T into the existing vertical drain, then immediately size down to 1-1/2" for the rest of the leg or do I stay at 2" until the stub out?

Also, here's my sketch for the sink piping. Is it acceptable?





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I am not a plumber but how will anyone use that cleanout that's facing sideways obstructed by a stud and eventually covered by finished walls?