Vent issue

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New Member
May 4, 2019
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Hi Everyone,

I have an issue about once a year in my upstairs bathroom where the shower backs up and bubbles start to come up out of the toilet (which also fails to flush when this happens). In order to get it working again it always takes an interesting combination of sinks and toilets flushing through the house and then all of a sudden everything drains (including the water from the toilet getting sucked down). I had a plumber out the first time this happened to witness and fix it. He said it must be a vent issue after it started working again and charged me $120 :(

I have pictures of the rough in plumbing and can piece together what I have. First, let me state that there is no roof vent on this run that I can find. It is entirely vented by two cheater vents under the sinks. The sinks are at the end of the line each having a cheater vent and draining into 2" PVC. I must assume these are 2" pipes y'ed into each other because I don't have that exact photo. The run takes a 90 deg bend and then the shower is y'ed in (also 2"). From there the line hooks into the toilet flange (assuming the toilet flange is also y'ed in) and the now 3" pvc turns 90 deg down and runs to the basement where one more 2" y comes in from another drain and then out to septic.

My theory is that I have some sort of air trap that is not allowing the pipes to drain. I believe by turning on the other faucets that I am creating a vaccum which breaks the air trap and allows the system to function again.

I am in the process of finishing my basement and will soon lose access to the plumbing. If there is something I can change down there to improve this, then I would like to do it while I can. What do you think?

Any and all advice is greatly appreciated!



Staff member
Supporting Member
Jan 20, 2018
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Boston, Massachusetts
if its just one bathroom and it happens once a year, I think its just a clogged drain just under that bath If it happens again try removing one of those vents and see what happens