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I noticed that my washing machine drain may not be properly vented: There is just an ABS pipe sticking up behind the laundry. In the basement underneath, it just goes into a cast iron sewer line that's shared with the adjacent bathroom sink:

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Here is how the pipe looks behind the laundry:

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Here is how it looks from the basement:

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You can see how the ABS pipe is connected to the cast iron pipe via a wye fitting (but no further connection). On the left end, the wye for the bathroom sink in my diagram can be seen.

Please note that the ABS pipe does not just stick up straight. As a matter of fact, it goes into the wall. Hence there is at least one elbow in the wall (indicated by the right angles in my drawing), but I do not think it's a p-trap: I tried sticking down a fishing tape with paper. I can clearly feel hitting an angle. Even when I push beyond the angle and then pull out again, it's bone dry. With a p-trap the paper would need to be wet, right?

Hence I believe this installation might not be proper.

On the other hand, in the 1.5 years of living here, I have never smelled sewer gas in this room. I also stuck no nose into this pipe and carefully took a deep breath: There is nothing that would smell like sewer gas.

Question 1: Does this require fixing?

Question 2: How can I best fix this without re-doing everything new?

One issue I see is that there is just not much room. Here is another picture that shows the ABS pipe sticks out not more than 1ft before going into the cast iron part:

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But not just with the length, it's tight in general: There is not much room for a p-trap. There are conduits, water pipes and wires closeby and the pipe goes up between two wooden beams, so not much room there either.

divB
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  • Depending on the code, the max standpipe height above its p-trap would be 30" or 42". Are you looking for code conformance? – popham Nov 01 '23 at 06:12
  • How far down did your fish tape go? Any chance there's an elbow next to a trap inside the wall? The distance would give you a hint as to that. – KMJ Nov 01 '23 at 16:35
  • @KMJ from the amount I stuffed in it went all the way down to the horizontal sewer line. Definitely much more than the elbow in the wall. – divB Nov 03 '23 at 00:09
  • @popham code conformance would be nice but in general first I don’t know how big the problem is. It seems there is no trap but I never smelled sewer gas. What could be the reason for this? And is this still an issue? I was hoping I can fairly easily fix it by inserting a p-trap in the basement (instead of the wye) – divB Nov 03 '23 at 00:11
  • Adding a trap without proper venting seems silly. I don't see any evidence of proper venting. The bathroom drain is your laundry line's vent, it appears. Fixing it would probably entail a p-trap running parallel to your laundry room wall and inside the wall, where the line would split to go down the drain and up to vent. For venting there's the bathroom's vent line (assuming it exists), a new vent, or an air admittance valve (if allowed in your jurisdiction). – popham Nov 03 '23 at 01:40
  • Ouch this is all getting so much worse than I thought :-( Question, can I replace the wye in the horizontal line in the basement with something like this: https://www.amazon.com/dp/B09Q6F5KD4 and then connect the ABS pipe that goes to the laundry standpipe to the output of the p-trap? – divB Nov 03 '23 at 05:41

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