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Question DetailsAsked on 8/19/2013

when tub drains air bubbles in toilet

when emptying the tub, it drains fine. But there are air bubbles that come up in the toilet. Do we have a vent problem?

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4 Answers


Yes. Is this a new house or did it just start? If you are a new owner or tenant there may not be a vent on the tub. If it just started the vent has a clog in it. Which is unusual unless it is a two story house with a bath above with a common vent. The clog could be anywhere and you will need a good drain cleaner to diagnose the problem. It cold be anything from a animal nest in vent on roof to something built up from connecting fixtures.

Answered 7 years ago by ContractorDon


If it is sucking the water out of the toilet bowl till it gurgles and goes almost dry in the bowl, then a plugged vent is almost certainly the cause, as it draws water from the traps to take in air that should be coming in the stack vent to replace the water volume going out.

Assuming the tub and toilet are adjacent to each other, one other possibility is a partially plugged drain somewhere below where the tub and toilet pipes connect. When you empty the tub, it would initially fill the sewer pipe above the blockage, and if the water flows out of the tub faster than it can down the sewer past the plug, the water level in the sewer pipe would rise to the water level in the tub (maybe a foot or few), forcing the air in the sewer pipe up the pipe to the toilet, where it could exit into the toilet as well as up the vent pipe, depending on where the vent is located. Would not be a lot of air, just afew cubic feet. If this is the case, when you flush the toilet the tub should gurgle too, and as the plug gets more clogged, pretty soon the toilet water will back up into the tub when the toilet is flushed. If you listen closely, air is probably coming up into the sink too - it will come up in whichever one has the shallowest trap.

Look at this image - you can see that if the blockage is between the toilet (in the drawing - could be tub more downstream in your case) and the stack, the air in the pipe when you flush or drain the tub that is displaced by the draining water has nowhere to go but up one of the three bathroom drains - tub, toilet, sink. -

Either way, you need a plumber - sometimes the two are one and the same, with a blockage at the wye or tee where the sewer pipe comes into the stack pipe if it was brought in below the toilet and tub pipes instead of upstream, as many plumbers do and the picture shows, and most codes allow if not more than a certain number of feet apart. Also, sometimes if you have a partial blockage (slow drain) below the stack entry, floating material will plug up the vent jusst above the wye or tee.

I would find a good plumber (Search the List if you don't have a good one already from prior needs), and I best routing the line from the toilet will clear the problem up.

Answered 7 years ago by LCD


Here is an almost identical question with answers that related to the same thing happening with a newly installed toilet - so another take on the situation if this applies to you.

Answered 7 years ago by LCD


BTW - when Contractor Don said you need a good drain cleaner, just so you aren't confused - he did not mean a liquid or crystal drain cleaning chemical - he meant a plumber or sewer and drain contractor.

Answered 7 years ago by LCD

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