Finally getting around to re-doing the powder room, and the boss has selected a pedestal sink. We suspect this space at the back of the house was an early addition since it has only a crawlspace, is not part of the full basement, but also was done in plaster/lath.

The location of the sink is on an outside wall, and the sill plate of the wall sits directly on the block foundation, so there is no way to bring plumbing up in the wall. So two questions if I bring the plumbing up thru the floor...first how do I run the drain through the floor without creating an S trap? Also what are my options for decorative supplies?



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Not a plumber by trade but a fierce DIYer

You can't.

You MUST have a vent.

? Is an AAV code permitted in your jurisdiction ?


Decorative supply: [www.plumbingsupply.com]

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

couple of ideas..
you can fatten up the wall behind the sink to allow the drain to come up in the new part. it can then vent straight up.
OR.. you can bring a drain and vent up in the new wall beside the sink. put a san tee facing the outside, 90 over to the center of the sink and 90 out the old wall.

I like packy's idea of making the wall deeper, build out another 2X3 or 2X4 so that the plumbing can come up through the footprint of the new wall, the OD of 2" PVC is 2-3/8" but the fitting will need more space, you might get by with 2X3 if you use 1-1/2" drain (if it's to code). That way you can plumb it conventionally with DWV and supplies. Take the deeper wall up may be 8" or so above the sink, the go back to the original wall, creating a notch that looks like an intentional design for storage of small bathroom items.



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Can’t the drain fall straight vertical from the tailpiece down beneath the floor, and then the trap can be located under the floor? For some reason I thought that would be code-compliant. I think I’ve seen it before I’m litchens.

Not legal to put trap under the floor.

"The vertical distance between a fixture outlet and the trap weir shall be as short as practicable, but in no case shall the tailpiece from a fixture exceed 24 inches in length"

Makes sense Steve, I would think if the tailpiece was too long, the water would have too much velocity going into the trap and it would self-siphon like an S-trap.

Packy I think your idea is best, and was thinking like sum suggested, a small ledge just above the top of the sink. I think I can get by with an additional 1-1/2" (2x2) depth since I do have some room on the edge of the sill. This will let me go with traditional supplies and trap set up.

Bernabeu I'm still not sure if AAVs are allowed in my town, but I've got 4 in use right now...I am thinking about running the vent up the wall behind the sink, adding an AAV, and one of these vented panels. I would then hang a mirror over the vent so you wouldn't see it, yet the AAV would still be serviceable. Is this a terrible idea?



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Not a plumber by trade but a fierce DIYer



Edited 2 times.

one of the seven ways a trap can lose it's seal..
SAMOBEC..

S) syphonage
A) aspiration
M) momentum
O) oscillation
back pressure
E) evaporation
C) capillary attraction

obviously the third item is what we are talking about here.. too long of a drop from the fixture to the trap..