Our house has two bathrooms (A and B) upstairs that are back-to-back on the floor plan. Both have showers, sinks, and toilets.

One day recently, when I was in an upstairs bathroom (A), the toilet in the other bathroom (B) was flushed by someone else. Immediately, the (A) toilet bowl burped bubbles up and drained out.

Shortly afterwards, we heard dripping above the ceiling immediately below toilet (B). Then, water poured out of the air supply vent in the ceiling.

Trying to troubleshoot before tearing things apart, I tested running water in different fixtures in both (A) and (B) bathrooms.


  1. Running water in either sink (A and B), caused both toilets to gurgle.
  2. Flushing toilet (A) caused toilet (B) to bubble a little from the drain.
  3. Flushing toilet (B) nearly overflowed it, but it eventually drained.
  4. All those fixture uses caused water to leak onto the ceiling below toilet (B).

However, running shower (A) and shower (B) was fine. No leaks. No gurgling. Interestingly, when I ran hot water in sink (A), my FLIR camera showed that the base of toilet (B) was hot.

Am I looking at a blocked vent? Bad toilet seal/flange? Broken drain somewhere? Clog somehow upstream of the showers in the same bathrooms?

Are the showers likely plumbed for their drains to join the main stack downstream from the toilets and sinks?

I’m stumped, and want to know just what I’m about to get myself into. Any ideas?

Edit: downstairs fixtures all work fine, without drainage issues or gurgling/bubbling/sudden draining/leaks.

  • Updated the question; someone else had flushed toilet B Commented Oct 10, 2023 at 3:12
  • Have you used a plunger on the nearly overflowing toilet?
    – popham
    Commented Oct 10, 2023 at 3:45
  • Not anytime recently, but frequently when my son still lived here :D Commented Oct 14, 2023 at 16:25
  • I've seen a squirrel drop delicious treats down a roof vent to block it at a constriction. Now that I think about it, I didn't actually see the squirrel. Could have been a false flag by a malicious neighbor.
    – popham
    Commented Oct 14, 2023 at 16:30

1 Answer 1


Showers and Toilets are on different drains.

Leaking toilet needs wax ring replacement.

The gurgling comes from blocked drain vent pipe (the one that goes true the roof. Clean it with plumbers snake

  • What if there's water coming from between the tank & bowl of the the leaking toilet? Will a wax ring replacement fix that? Since we don't know where the water's coming from, such a bold, blanket, unconditional statement seems a bit... asinine. How do you know the showers and toilets are on different drains? Maybe the showers are just downstream of the blockage. Maybe the showers have separate vents or distinct routes to the vent that's not blocked?
    – FreeMan
    Commented Oct 10, 2023 at 14:22
  • 1
    In this case, the water isn’t coming from between the tank and bowl. It’s coming from somewhere under the bowl. Commented Oct 14, 2023 at 16:26
  • @DustinMiller as I said in my answer, it is the wax ring. You can hire a handyman, or do it your self
    – Traveler
    Commented Oct 14, 2023 at 18:10

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