enter image description hereHello,

Can someone please help me identify the rough in pipes in my basement?

Is 1 the vent that I can tap into for a sink, 2 is the toilet and 3 a shower?

Or is 1 strictly a vent, 2 a toilet and 3 a sink?

Any help would be greatly appreciated!

  • 1
    2 is toilet for sure. 3 looks like a shower drain, but to make sure pop it open and pour some water down it. If it is shower drain should have p trap in the slab so water will collect. 1 could be vent stack, probably wet vent for the whole bathroom. If so you can attach sink to it. Is there vent connection roughed in the ceiling? Nov 4, 2023 at 14:43
  • No vent stack to tap into above. Theres the vent for the water heater above, but I’m pretty sure I can’t tap into that.
    – Dctasson
    Nov 4, 2023 at 15:52
  • Yea that sounds like an exhaust vent for the water heater. Which is completely different thing. It's weird to have the rough in in place but no vent tie in. Do you have contact to original builder? Otherwise you'll have to open up walls and ceilings to put in a vent. Nov 4, 2023 at 16:12

2 Answers 2


I'm going to take a guess. Obviously, that's all we can do with pipes already buried in concrete.

It looks like there's a sewer riser in the corner behind the ladder, and it looks like there's a main cleanout in the floor near the camera.


My guess is the 2 and 3, toilet and shower, are wet vented through the riser in the corner. I don't know if that's ok to do with the 10 feet or so of horizontal pipe between them ... question for a code expert.

1, the sink, needs a vent because otherwise it's a nasty S trap. So my guess is the riser there is to be connected to the riser in the corner, at ceiling height. I drew it lower to stay in the shot.

enter image description here


Contact the contractor. Even if you're on bad terms, they should still inform you on something like this. Assuming you're on impossible terms with the contractor....

Under the International Plumbing Code (you should figure out what code governs your work), a wet vented bathroom group requires 5 or 6 drain fixture units depending on the gallons per flush of the toilet. See IPC 709.1.

According to IPC 912.3, 2" pipe is sufficient for wet venting 5 drain fixture units. If pipe 1 is 2", then it's a coin flip whether it's a wet vent. Contact your building department and get a copy of the inspection report. In my city the inspector's handwritten notes will often mention "wet vent" explicitly.

Again according to IPC 912.3, 2-1/2" pipe is sufficient for wet venting 6 drain fixture units. If pipe 1 is 2-1/2" diameter, then, 95% chance or better that it's a wet vent. If you want 100% certainty, then contact your building department.

Worst case scenario, you can stick an endoscope down there. It's pretty cheap, and it's a fun toy to have laying around.

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