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Old 04-20-2017, 08:40 PM   #1
olegus
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Default Air bubbles in the toilets

My toilets sometimes let go a one or two air bubbles when flushing. Home inspector came and suggested to check vent pipe on the roof. Everything else works fine - sinks, buthtubs drain fine, no gurgling sounds, no water backouts. Called plumbers, described symtoms - they suggested don't bother. But what will be a reason for these bubbling? All equipment is about 20 years old. Is it a way to get rid of them?


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Old 04-21-2017, 04:59 PM   #2
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My toilets sometimes let go a one or two air bubbles when flushing.
Water enters the bowl from the rim and from a small hole directly across from the exit hole. I think it is called the jet hole, its purpose is to get the water in the bottom of the bowl to start moving out the drain. It might be possible for some toilet models to end up with a substantial amount of air in the top of the channel which feeds the jet hole. If that is happening on your toilet then when you flush the sudden inlet of water from the tank traps and then pushes that air down through the remainder of that channel and then out the jet hole, where you see it as some bubbles. The same sort of air motion could be happening in the tiny rim hole channels but you would never see it there.

Anyway, I suggest you look closely at the bottom of an empty bowl when it is flushed and you will probably find that the air is coming out of the jet hole. In which case, I wouldn't worry about it.

This is assuming you have a conventional toilet.


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Old 04-21-2017, 05:43 PM   #3
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Anyway, I suggest you look closely at the bottom of an empty bowl when it is flushed and you will probably find that the air is coming out of the jet hole. In which case, I wouldn't worry about it.

This is assuming you have a conventional toilet.

Will do, thanks for the thorough explanation. It does not look like vent problem to me and I am glad you did not mention it too.
But I'm just curious here- what will be other symptoms of obstructed vent pipe?
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Old 04-21-2017, 07:01 PM   #4
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Old 04-22-2017, 04:16 PM   #5
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But I'm just curious here- what will be other symptoms of obstructed vent pipe?
I have never had that problem at any of my homes. According to various web sources you might encounter:

1. slow toilets, sinks, tubs
2. gurgling sounds
3. sewer smells (because the water in the traps can be sucked out)

Those are pretty much the same as a partially clogged drain. Signs of actual backing up, like the toilet bubbling when the tub empties, are going to be clogged drains. The toilet "ghost flushing" under the same circumstances would be a trap issue. (Tub water emptying creates vacuum which sucks water out of toilet.) Another differential diagnostic is if a downstream sink is slow, and an upstream sink's trap is removed, then the downstream sink will work normally. Personally that sounds like more work than going up on the roof and hosing out the vent pipes.
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Old 04-23-2017, 11:15 PM   #6
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Your symptoms are NEVER caused by any kind of clogged vent pipe. Unfortunately this is a theory that is popular on the internet and often mentioned when this type of problem comes up. One of the most classic examples of "I read it on the internet, how can it not be true?" Well, it is not true. Your symptoms are always caused by partial clogs. Either the built-in toilet trap is clogged or your downstream drain pipe is. Snake out the clog, toilets will not "bubble" anymore.
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Old 04-24-2017, 02:46 AM   #7
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A vents ONLY job is to protect the seal of the p trap

all a vent does is cause the pressure in the plumbing system to be equal on both sides of the trap when the fixture is draining
without the vent, the pressure in the pipe when the fixture drains would be negative.
causing the P trap to siphon dry
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Old 04-24-2017, 07:00 PM   #8
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A vents ONLY job is to protect the seal of the p trap

all a vent does is cause the pressure in the plumbing system to be equal on both sides of the trap when the fixture is draining
without the vent, the pressure in the pipe when the fixture drains would be negative.
causing the P trap to siphon dry
I wonder how often there would be symptoms even with a completely sealed vent.

My tub drains through a 1.5" (presumably) pipe which Y's into the common 4" drain pipe. Any traps upstream from that point might in theory be siphoned when the tub drains, but that's only going to happen if water completely fills the 4" drain pipe, otherwise there is an air connection all the way to the sewer at ambient pressure. Since the big drain is fed by a 1.5" pipe, which restricts the flow, and the 4" pipe is not clogged, the big drain is never full across with water. The amount of water from a sink or another toilet flush is so small that these will never fill the main drain either.

Only if in addition to the full vent clog there was also a partial clog in the drain would I expect to see the siphon action. But in that case the toilet would at least bubble every time the tub was emptied, if not outright overflow.
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Old 04-24-2017, 07:49 PM   #9
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that is assuming no other pipes are connected to the 2''

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try this, glass of water, put a straw in the water, place finger over end of straw and lift

the water stays in the straw...no vent
remove finger. vent


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