Related to Can I tap into the kitchen / dishwasher drain pipe with my washing machine?, but not the same.

I want to plumb a dehumidifier into a drain for a bathroom sink on the other side of the wall. I just cut into the wall on the dehumidifier side (looking for a leak; it turned out to not be leaking).

inside wall

The pipe heading off to the right at the bottom is the sink drain. the P-trap is under the sink, on that far side of the wall. I am not clear what the pipe going up goes to, as there is only attic above (might be AC drain?).

I want to bring a port through the wall, in a way that I can run the dehumidifier discharge hose directly into it. How can I best do that?

1 Answer 1


The pipe going up is most likely a vent. If you're going to start doing plumbing, you should take a bit of time to understand that vents are important to your drains working without making your house stink.

They provide a path for sewer gasses out of the house, and they prevent siphoning the water out of the traps that keep a barrier of water between sewer gas and your house.

If you want to add a drain, you need to add a trap for that drain. Because if you don't, you'll get sewer gas in the house. Typically that involves adding a sanitary Tee to the vertical drain pipe, or a Wye to the horizontal drain pipe, then a trap adapter to the inlet of the Tee or Wye (or pipe, not too long attached to it) then a trap to the trap adapter.

  • Clear on the need for traps. Is there a thru-wall part that I should be looking at?
    – fectin
    Commented Nov 15, 2023 at 3:27
  • 1
    wall flange pr escutcheon if you want to make it look fancy. the trap adaptor is the part that connects the tail of the trap to the drain pipe and often sticks only a short way out of the wall.
    – Jasen
    Commented Nov 15, 2023 at 12:54
  • @jason looking at using an in-wall air admittance vent box, plumbed like a washing-machine drain.
    – fectin
    Commented Nov 26, 2023 at 20:52

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.