So here's some plumbing in my house (not done by me):

This was before I sealed everything up behind drywall. The drain is actually used for a Cat Genie, our laundry is in another room.

Now we're having an issue where the drain is not draining quickly enough, sending gross water from the fancy flushing litter box onto the floor.

I've got an endoscopic camera down to the wet trap and didn't see anything amiss, but before I tear into the drywall, I was hoping someone could tell me -- does this plumbing job look acceptable? Do you think my problem is here or downstream?

The venting you see is into the wall -- this is on the first floor, getting a vent all the way to the roof in this 80 year old house would be a Herculean task.

Any pointers appreciated -- I do ok with electrical, but other than decent skills with PVC, plumbing isn't my area of expertise.

  • 3
    I don't know about the plumbing, but that orange cord sure looks like it belongs to an extension cord. If that's what it is, it is not code compliant for permanent use sealed up behind a wall, and likely not safe for use like that.
    – Johnny
    Dec 30, 2015 at 7:07
  • 2
    The vent is in the wall?! That means deadly sewer gas could be (probably is) dumping into your home. Also, if there's a problem, sewage could be expelled into the wall cavity.
    – Tester101
    Dec 30, 2015 at 10:00
  • 2
    @Johnny Orange cable could be (and likely is) 10 AWG NM-B cable, not an extension cord. If that's the case, there's no problem using it. However, the cable should be secured in place using staples, or other approved means.
    – Tester101
    Dec 30, 2015 at 10:02
  • @Tester101 - Yeah, it could very well be NM-B, but 10-3 typically looks fairly flat (10-3 is usually rounder), and the pictured cable doesn't look very flat. I brought it up because I saw almost the exact same setup in a house where the homeowner added laundry to the garage and used an extension cord running up the wall to the attic then down to the furnace closet -- with a 3 outlet adapter plugged into his single furnace outlet so he could plug in the extension cord.
    – Johnny
    Dec 30, 2015 at 18:04
  • @Johnny It looks like NM to me. If you look close, you can see the wires twisted under the sheath (especially right near the sanitary tee in the photo).
    – Tester101
    Dec 30, 2015 at 19:00

2 Answers 2


I'd say the standpipe is a bit short, though I think 24" is minimum code. If the p-trap is clear, then possible issues:

  • there's a clog further downstream
  • the cat toilet is simply expelling too much water too fast
  • the vent stack is plugged

It's not a great fix, but one potential solution is to install a wash basin and connect that to the p-trap instead. Then have the cat toilet dump into the sink. That way the wash basin can completely fill and slowly drain.

  • If I recall correctly, minimum standpipe height is 18" above the trap weir. But I could be mistaken.
    – Tester101
    Dec 30, 2015 at 9:56
  • Thanks. I don't know how high it goes, but it goes well beyond what is visible in the photo. The kitchen sink in on the same line and drains well and the cat toilet only uses maybe a gallon of water at a time, so it sounds like it's time to open the wall (fortunately now behind a floating cabinet) and check the p-trap and vent. (I'll also install an air admittance valve on the stack if there isn't one.) Jan 1, 2016 at 7:51

If the vent pipe is sealed in the wall, that means you have no vent. once that area slightly pressurizes it will start having trouble draining. If the system drains fine with the wall open you really need to vent to the outside. I would not want an open vent inside my house, I have read about vacation houses blowing up when the toilet trap dried out and methane sewer gas was ignited by a pilot light.

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