I am new here and hope to get help.

Some years ago an amateur plumber installed a new toilet in my basement and he did not install a vent. The toilet did not flush, and I installed an air admittance valve, as illustrated in the following drawing.

enter image description here

I assume nobody did this, but it worked, until recently. I took away the aav, and it flushed very well. I bought a new aav, and put it there, but it did not flush.

I added another aav below the sink, which is just two feet away from the toilet, but it did not help. The aav won't help the toilet to flush.

enter image description here

I wonder what the problem or problems are. Why the old aav worked and now it stopped working? I took away the aav, old or new, it flushed perfectly. I also do not understand why the newly added aav does not help.

I would like to know how to solve the problem.

  • 2
    You probably now have a plugged drain.
    – Gil
    May 15 at 4:05
  • If plugged, not totally, because water still flushes when the AAV port is open. I am thinking maybe the slope is not right, and thus the water is hard to go to the drain line May 16 at 15:37

1 Answer 1


I can't remember the manufacturer name, but I encountered one brand of AAV that had a seal that you had to remove prior to installation. It was a soft plastic piece that kept the valve from moving around during shipping and prematurely wearing out.

Check your valve for such a seal. If you have the original packaging, it was noted there and on the instruction sheet inside the box.

  • The brand is Oatery and there is a plastic wrap that functions to prevent it from moving around, I guess. I peeled off the plastic before installation and I saw no other places that seal it. Thank you very much for your answer, but do you think what other causes may exist? May 15 at 14:45
  • If it works with the AAV off and doesn't work with the AAV installed, you either installed it incorrectly or the AAV is defective. I can't think of anything else that would do it. If it doesn't work with the AAV removed, you have another drain problem you need to locate.
    – KMJ
    May 15 at 16:02
  • Can a new AAV be defective? May 15 at 19:27
  • Everything can be defective. Most likely though, you missed something when installing.
    – arne
    May 16 at 9:27

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