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I am renovating a bathroom and the drain is coming from the side. This was done because the vent stack is on that side wall. The wall directly behind the vanity would be an outer wall.

I am planning to put an Ikea Godmorgan vanity with drawers. I would like to move the plumbing to the back so there is no interference with the drawer. Since its an outer wall, I prefer not to go behind the wall, instead go down through the subfloor.

  1. Would the proposed new drain run be viable? (would it be vented, up to code, etc.)

enter image description here

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    Edited to ask the more pressing question. I did briefly read that post, then lost the page and couldn't find it. I know the important part is the drain being vented. Which I believe in this case it is, but I just wanted advice from more experienced plumbers. Dec 27, 2022 at 19:42
  • ... and revise your title to ask a clear, specific question.
    – isherwood
    Dec 27, 2022 at 19:47
  • How is the toilet vented? It looks like 6 or 8 feet to the vent.
    – jay613
    Nov 24, 2023 at 18:39
  • You are looking at a wall-mounted vanity that does not reach the floor. It is meant to have in-wall plumbing. You say you don't want to put plumbing in the wall because it's an outside wall. So you'll have pipes coming out of the floor, in open view? Maybe you should choose a different vanity that give you better options.
    – jay613
    Nov 24, 2023 at 18:41

3 Answers 3

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What you draw won't work, if you want it all to come out of the floor you'll need to do an island vent or use an AAV if one is permitted in that location.

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Depending on your code in force, there is a way to do something like this and still vent properly. In my case, this section is struck from locally adopted code, so I could not do it.

"The trick" is that the downward pipe from the trap is 2", ensuring that a 1.25 or 1.5 inch lavatory drain can't make it siphon. There are also limits on distance.

IPC section 917 "single-stack vent system" for details. More importantly, check your local adopted code which may or may not be based on IPC and may or may not include this section or a similar one. It's evidently baed on a Philadelphia code with over 100 years of successful use, and was adopted in IPC in 2012.

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Unfortunately, the way it's vented in your drawing won't meet code. Your vent is going to have to branch across and tap into the horizontal run out of the P trap - probably where it goes vertical, using a sanitary tee.

The rule of thumb is that the trap weir in the P trap needs to be able to 'see' the vent.

enter image description here

There are also code regulations with minimum and maximum distances that the vent must be from the P trap based on the drain pipe diameter. For example, for a 1 1/2" diameter drain the vent must not be closer than 3" to the trap nor more than 42" away.

Option 2: You could possibly run the P trap to the right and take it directly into the wet vent in the wall on your right. The issue will be working around any drawers/shelves - maybe behind a drawer?

Option 3: As mentioned in another answer here you might check to see if an AAV (air admittance valve) can be used under a vanity in your locale.

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  • Bummer. I thought since the stack was a 3 inch, and the drain would be 1-1/2 inch, that would be good. Dec 27, 2022 at 20:43
  • You may find it easier to run the P trap to the right and tap into the wet vent in the wall. I edited my answer to include this option.
    – HoneyDo
    Dec 27, 2022 at 21:16
  • there isn't that much space to make the connection. See picture here: imgur.com/a/I5RwKdw Dec 27, 2022 at 21:22
  • Not sure what the pic is showing us. Looks like a wet vent on the left side of the pic. Maybe a pro plumber will jump on here and come up with a better solution.
    – HoneyDo
    Dec 27, 2022 at 21:36
  • That imgur picture is the original plumbing. That ABS pipe on the left is the vent stack. Where the Tape measure is touching is the exterior wall. Dec 27, 2022 at 21:55

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