Mystery Toilet Tank Back Pressure Gas


For many years at the beginning of the month I have gotten calls from people who tell me their toilet partially empties and refills in the middle of the night.

Most of the time they want the tank drain flap replaced. Many times the tank flap is in fine shape and does not necessarily need to be replaced.

Finally, in 2005, I was able to capture on video a toilet tank emitting so much bubbling gas the tank flap could not shut.

My solution was to turn the water off and check later in the day to see if it stopped. It did. And there was no more trouble after that. But I still have no logical explanation.

So, today, from the Pottyology archives my captured video of an unsolved mystery.

What you see here is gas in the toilet tank with enough pressure to keep the tank drain flap open.

Most knowledgeable people (me included) will tell you the design of a toilet makes this type of bubbling gas pressure virtually impossible.

Any engineers with any explanations?

  1. Eric said:

    Maybe a plugged vent stack would prevent the sewer gas from escaping that way, so it took the only way it could. It seems that it would be easier to bubble up through the sink, though.

    • handyguy said:

      What ever caused this self corrected after the water had been cut off for a few hours. Any blockages in the vent, the sewer or anywhere else would have had to have been temporary.

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