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Similar to many others, I'm installing a new sink that is significantly deeper than the one it is replacing. Due to added sink depth and the location the builder chose to install the original drain - I believe I need to lower the drain so that the waste can properly drain.

After the new counter top, undermount 10" deep sink, and garbage disposal, I've determined that the garbage disposal drain will be about 1/2" below the center of the waste drain.

I've determined that the drain is a dirty arm (horizontal style) drain instead of a more traditional trap drain (vertical style).

How would one go about lowering the drain 3" or so specifically with this dirty arm setup? Tearing into the wall under this cabinet is not a problem, but access to the left of the cabinet where it appears the sanitary tee is would be a significant challenge.

Sink Plumbing Issue

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  • @Alaskaman - Thanks for the comment. I am not 100% sure that moving the outlet at the wall is necessary until (as you said) the new sink is in place. But I think that it will be close enough and I figured it would be safer to just move the drain at the wall to get ahead of any possible issues after the counter top and sink are installed - thus my question about moving the actual outlet. If I'm way off on this, let me know.
    – dpollitt
    Commented Mar 7, 2017 at 3:28
  • How you lower the outlet will depend on where it's going. If it's passing through several studs, then you're either going to have to cut 3" out of each stud, or re-run the outlet lower in the wall for as long as it's traveling horizontally. You best hope you don't have to lower it, you're likely going to be opening up the wall if you do.
    – ShemSeger
    Commented Mar 7, 2017 at 3:53

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I ended up following Alaska Man's advice and lowered the sanitary tee. After installing the new sink and the disposal, it was obvious that my only option was to take the sanitary tee route. The good news was that I did have access to the other side of the wall so getting at the tee was simple. The unfortunate news was that I really only needed to lower the DWV about an inch.

Here is what my disposal looked like after install - showing the DWV too high by just a bit. The after shows how far I lowered the DWV. Disposal too low

On the other side of the wall, this is where I lowered the sanitary tee about 3 inches total. Sanitary tee

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You can use the shortest possible tailpiece on the drain basket and shortest possible section of pipe that is below where the disposal pipe comes in and slips into the trap. (There may be a trap that is not quite as deep as the one you have.)

If that does not get you there then lowering the sanitary tee or shallower sink.

You can not move the waste drain down without moving the san tee. You would need to open the wall cut the drain/vent and move the sanitary tee down and then drill new holes in the studs for the dirty arm.

Or possible turn the san tee so it comes straight out of the wall and then plumb to it without messing with studs.

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