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I have a very space-limited situation for a bathroom sink.

My 4" vent stack is inside the wall immediately to the left of my sink (~18 inches away, probably less).

If my sink's tail piece is close to the wall such that end of the p-trap ends inside the wall, would it be against code to run from the tailpiece, perpendicular to inside the wall with the p-trap, and then from the p-trap turn 90 degrees and connect it to the stack directly without adding a vent? This doesn't add any additional bends or turns, it just changes the direction that the exit of the p-trap is pointing (90 degrees perpendicular instead of parallel).

Code dictates that a vent has to be within a certain distance of the p-trap, and the stack is well within that distance. I can't go up to vent above the fixture flood level because there is a vanity mirror in the wall blocking. I'd like to avoid adding a Studor vent if I can.

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So long as it is at least 2 pipe diameters from the trap weir to the vent pipe... Closer than that is forbidden (crown venting) as is too far.

Depending on the arrangement of parts, sometimes pointing the P in a different direction than "right at the wall" and using the swivel joint on the outlet pipe to head back in to the trap adapter makes things work better.

If the tailpiece extends into the drain pipe, cut it off (not too too short, enough length to allow for some adjustment, without it sticking into the drain/vent stack. They come long, they are supposed to be cut down as needed. So if you assemble it and set the ring seal, you can then disassemble and cut it off perhaps an inch after the ring seal position.

But 18" is not particularly tight...

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