I have a bathroom with a bathtub, toilet, and sink that are all very, very slow to drain. When water drains out of the toilet, it backs up into the tub, and vice-versa.

Here's what the setup looks like.

        Sink   Toilet   Tub
 < Flow of water <    |
                  Clean out

To the right of the tub there is nothing.

Here's what I've tried:

  • I had someone (not a professional) auger the clean out and remove some solids (looked like food from the garbage disposal and soap scum).
  • He removed the toilet, took a hose, and sprayed water into the drain and the water went through the drain pipes no problem. After he put the toilet back on, the problem seemed to be a little better, but still noticeably slow.
  • Putting some enzymatic stuff in there over the course of a couple weeks
  • Putting Liquid Plumber down the tub drain and sink
  • Putting bleach down the tub drain and sink

What else can I do (short of calling a plumber) to troubleshoot this?

  • Can you get to any inspection covers downstream of the sink? Commented Jan 2, 2015 at 19:46
  • No, unfortunately. The clean out that is under the bathroom was actually put in by the guy that augered the pipes because there wasn't one there.
    – Ben
    Commented Jan 2, 2015 at 20:23

2 Answers 2


Clearly the restriction is left of the sink in your diagram. One more question you could consider is whether this is an installation deficiency (problem has always existed) or whether the drain was working properly at one time and the situation has become worse.

I would suggest using a video inspection camera to be certain about the location of the restriction and perhaps what is causing the restriction. Here is a rental unit that may be available in your area. Or here is a contractor that could provide this service. It would be best to try to clear debris before the blockage prior to a camera inspection.

  • I suspect it's an installation deficiency. When I first moved in, the drainage was slow, but not to the point that it was a problem. Then it got progressively worse.
    – Ben
    Commented Jan 2, 2015 at 20:28

Coule be an air problem in your pipes.

In order to check this:

  • Flush the toilet, make sure it is very slow as usual.

  • Remove an easily accessible u-bend like the one below the sink to vent the drain pipe to atmospheric pressure.

  • Flush the toilet again and check if it goes faster than the first time or not.

If this time it drains normally, then you got an air problem, possibly on top of something clogging the pipes somewhere. But it could be just air trapped in the pipes between your bathroom and another U-bend down the line. In this case a vent will have to be installed where it is convenient.

  • Your diagram does not show a vent pipe which is generally required by code. Is it physically there but plugged? If so clean it out and your problem will go away, If it is not you need to add a vent as indicated by bobflux.
    – Gil
    Commented May 29, 2021 at 16:30

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