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I have the current setup in the basement, as shown in the photos below. I would like to see if any wisdom can be shared here to add a proper drain for the washer, i.e., a 18" standpipe with a p-trap that stands at most 18" above the ground.

Right now, the clean out plug is on the right side of the double wye, placed just on top of the main drain. There's no way to add anything below the double wye down the main drain pipe.

I'm completely new to plumbing. I have a perhaps-crazy thought on

  • extend from the wye on the right at 45 degree, add a MPT x Hub
  • still at 45 degree, add a tee with the side inlet facing the wall
    • at the end of the 3" Hub, add back the screwable plug
    • from the side inlet, make a 90" turn with an elbow so that a horizontal pipe can go to the right. With this particular fitting, the 2" inlet can point up
      • the horizontal pipe will be reduced to 2", and be finally connected with a ptrap and standpipe.
      • the 2" inlet will go up, then to the left, going behind the vertical drain, and finally connect to the vent pipe on the left, above its current clean out.

I tried to visualize the above but I failed to draw it in 3D. So I hope people can understand what I said over there. May be it's crazy, violating some code. Please feel free to point out anything that might be wrong. A new/better plan is welcomed too.

p.s. I hesitated to stack a cleanout tee on top of the double wye, because cutting it seems to be way messier than extending from the existing clean out. Now: enter image description here Now: enter image description here

Proposed (flipped, assuming viewing from the wall): enter image description here

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    That looks like a good solution to me. I've done a similar project and wasn't fortunate enough to have an existing vent out the roof. You've got an easier task. I'll let someone with more code knowledge answer.
    – isherwood
    Commented Dec 16, 2020 at 20:38
  • I like your plan. Be sure to do a dry-assembly of all the new DWV to make sure everything works before you start applying solvent. The part I would suggest trying another way is adding a Wye to the existing one to connect to the new branch drain. I may be confused about how you plan on doing it, but this is the fitting I would try: (street) supplyhouse.com/… or (all hub) supplyhouse.com/Nibco-I090550-3-Hub-ABS-DWV-45-Wye-5810 Commented Dec 17, 2020 at 0:49
  • @JeffWheeler I believe you're suggesting to use a Wye instead of the Tee I proposed there. Is it because of any code requirement?
    – loclos
    Commented Dec 17, 2020 at 7:41
  • @JeffWheeler And by adding a Wye to the existing clean out, should I similarly use the straight end as the cleanout replacement, while the angled inlet will be used to branch out? If so, which direction will the angled inlet go? I'm confused too :)
    – loclos
    Commented Dec 17, 2020 at 7:50

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Not a plumber but redid my basement washing machine drain last year. Just some things to keep in mind off the top of my head. Remember that it's a good idea to introduce a small slope in horizontal vent runs, so that any condensation can drain happily back into the drain system.

Also note that, depending on how high that p-trapped sink is, you might be creating a new low point for sewage to back up into your house if there's ever an issue in the street. It's an unlikely scenario, but when I did mine, I included a PVC backflow preventer valve just in case.

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