I found a similar thread, but kind of old. Looking for ideas for my particular situation.

You can see in this picture that our nice new vanity doesn't leave room for the p-trap when making the drain connection. I understand that simply adapting up can create issues with the p-trap being siphoned? This is not a cheap vanity and my woodworking skills are not the best, so I'm quite hesitant to hack a hole in the shelf. The only other thing I can think of is to rip open the wall and raise the connection?

enter image description here

Here's the previous thread, which I think settled on cutting up the vanity:

Drain trap is too low for new vanity

  • How high is that bottom shelf from the floor? I believe it will be much easier to cut an access hole in that shelf/floor than to raise the drain pipe. Mark out a neat square hole to fit the p-trap and give yourself enough room to place it without skinning your fingers.
    – crip659
    Nov 18, 2023 at 18:25

1 Answer 1


ASTM D3311 specifies that the trap of a 1-1/4" p-trap must sag at least 3-3/8" from center of outlet to center of the trap's low point. ASME A112.18.2 prescribes performance standards instead of actual dimensions, so you might be able to find a shorter yet still conformant p-trap by scoping your searches with "ASME A112.18.2".

To avoid siphoning, the pipe can fall no more than its diameter before it reaches its vent. Assuming that the trap sidewall thickness is the same as the pipe's sidewall thickness and assuming that your drain's vent is immediately behind the wall, then, the lower edge of your pipe at the wall outlet must be higher than 3-3/8" - 1-1/4" = 2-1/8" to avoid siphoning.

Your wall outlet is obviously too low, so it looks like you're stuck cutting into your wall. Unless you can find a short trap that conforms to ASME A112.18.2, but I'm pessimistic on that prospect. With a hole saw and some precision, you could cut the shelf nicely. I suspect that 2 well placed holes would allow installation of the trap going through the bottom of your vanity without connecting the holes to make a slot. The AAV from your linked question is also an option, of course.

  • Or cut a hole in the bottom of the cabinet?
    – Huesmann
    Nov 19, 2023 at 14:30

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