# Bubbling in toilet



## rballard (May 9, 2008)

I have a rental property I'm just getting ready to have new tenants move into. While running the water in the bathroom sink, I noticed the toilet water started bubbling. I turned the water off and the bubble stopped. I turned the bathtub on and the toilet started bubbling, then stopped when I shut the tub off. Why would this happen? And more importantly, how do I make it stop?


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## Nestor_Kelebay (Jun 17, 2008)

It sounds to me that this is a basement toilet that was added after the house was built.

In a case like that, the building code won't require the homeowner or contractor to tear the house walls apart to install another vent stack through the walls to the roof. It will only require that the toilet be connected to the main drain line coming from the house.

Now, imagine that main drain line is quite badly clogged, and water backs up that drain line all the way to where the basement toilet connects to it.

In that case, if ANY of the faucets in your house put water into your house's drainage piping, water is going to back up in the drain line from the basement toilet.

The air that's displaced would normally be pushed harmlessly up the vent stack behind or beside the toilet.

However, if this is a basement toilet was added after the house was built, there won't be a vent stack. In that case, the pressure in the drain piping will build up until air bubbles out the toilet bowl water.

If it were me, I would have the main drain line from your house snaked (or otherwise cleared) to remove the partial clog. Without a partial clog, then no water will back up into the drain pipe servicing that basement toilet.

Drain pipes gradually clog up with solids (mostly from the kitchen sink) even with just normal use. However, it may be that a former disgruntled tenant left you a gift by flushing a pair of blue jeans or some other darn thing.

Maybe flush your toilet when that happens, but be ready to take the lid off and close the flapper if it looks like the toilet bowl is gonna overflow.


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## rballard (May 9, 2008)

The toilet is not located in the basement, it's on a third floor. There is no vent system, although here in PA it's not totally uncommon and there's no one going around to check if things are up to code. I could try snaking or having the main snaked, but it's quite long... as in three full floors +.


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## majakdragon (Sep 16, 2006)

If you didn't have a vent system, none of the fixtures would drain properly. Look on the roof for a 3" or 4" pipe sticking out about a foot or so. This is the vent pipe. It may have leaves or a birds nest in it. Remove all you can by hand and then flush with a garden hose. The vent pipe is merely an extension of the main drain line that goes through the roof to allow air to enter, which is needed for proper drainage. Click on the link below and scroll down to the picture. This is a typical drainage system. look at where it exits the roof. this is the vent.

http://www.hometips.com/hyhw/plumbing/74drain.html


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## Nestor_Kelebay (Jun 17, 2008)

majakdragon said:


> If you didn't have a vent system, none of the fixtures would drain properly...





> that goes through the roof to allow air to enter, which is needed for proper drainage.


Majakdragon:

I always thought that the purpose of venting was to allow air in behind the draining water to quench any vaccuum created which might otherwise suck the water out of the p-traps. 

When you drain a bathtub, would air be entering the drain pipe? I woulda thought that if anything, the water level in the vent pipe would equalize with the water level in the tub. That would require that water enter the vent pipe rather than air in the vent pipe enter the drain pipe.

What am I missing here?


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## Alan (Apr 12, 2006)

Nestor_Kelebay said:


> Majakdragon:
> 
> I always thought that the purpose of venting was to allow air in behind the draining water to quench any vaccuum created which might otherwise suck the water out of the p-traps.
> 
> ...


water WOULD equalize in the vent if there was a clog or partial clog slowing the flow. That is why vents are taken off vertical. Water should never flow into the vent, unless there is a clog. But, as water flows out of the fixture, into the trap and trap arm, the water fills the pipe and therefore needs a place to push the air out. Without the vent, it would continue down the pipe, and suction created by not having the vent would suck the water completely or partially out of the trap allowing sewer gasses to enter the house. 

this seems to me like exactly what you just typed only elaborated... i've been drinking so i hope it even makes sense. :huh:


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## majakdragon (Sep 16, 2006)

Nestor, You are correct. The vent allows air in behind the water. There are 2 connections to the vent for each fixture. One is at the main drain which is also the main vent. The other is a ventline connected just after the fixture trap and then rises up and over to the main vent. When a tub or any other fixture is draining, the vent does not fill up with water since the water is going into the drainline which always is below the fixture. If it had no vent, the water would "air-lock" and not go down the drainpipe until the fixture was empty and the traps sucked out to let air in. It "would' drain, but very slowly and with heavy bubbling. Since the vent goes out the roof, it can never fill with water and will alway be able to have air flow down it to assist drainage. Hope this helps. The link I posted for the original poster may let you see what i am talking about.


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## Alan (Apr 12, 2006)

majakdragon said:


> Nestor, You are correct. The vent allows air in behind the water. When a tub or any other fixture is draining, the vent does not fill up with water since the water is going into the drainline which always is below the fixture. If it had no vent, the water would "air-lock" and not go down the drainpipe until the fixture was empty and the traps sucked out to let air in. It "would' drain, but very slowly and with heavy bubbling. Since the vent goes out the roof, it can never fill with water and will alway be able to have air flow down it to assist drainage. Hope this helps. The link I posted for the original poster may let you see what i am talking about.


the vent for the toilets on that picture needs to be upsized as the 1st toilet connects with the 2nd according to my code. :thumbup:

of course... that really has no bearing on the current conversation. lol


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## majakdragon (Sep 16, 2006)

Alan. It's 4". If that isn't big enough....it's 6". Just kidding, but the drawing was just for laying out drains and vents, not code. In all the States I have worked in, two story only needs 4" main drain/vent even with 3 toilets installed.


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## Nestor_Kelebay (Jun 17, 2008)

> Nestor, You are correct. The vent allows air in behind the water.


OK, good. That much we agree on.



> There are 2 connections to the vent for each fixture. One is at the main drain which is also the main vent. The other is a ventline connected just after the fixture trap and then rises up and over to the main vent.


Don't we really only have ONE connection? That being that the vent pipe connected to the drain pipe just down stream of the trap.

My understanding is that the only reason why the vent pipes from each fixture connect to the vent stack under the roof is to minimize the number of roof penetrations to keep possible roof leakage sites to a minimum. The fewer roof penetrations there are, the fewer places where the roof is likely to leak.

The other end of the pipe being connected to the vent stack isn't significant in any way. In order for air to flow from the vent into the drain pipe, it has to come into the vent pipe somewhere. If those vent pipes weren't connected to anything, and were simply capped off, there'd be no point in having vent pipes.



> When a tub or any other fixture is draining, the vent does not fill up with water since the water is going into the drain line which always is below the fixture.


I'm thinking that a full bathtub and an empty vent pipe be a violation of the laws of physics. The pressure at the vent pipe connection is going to be the hydrostatic pressure of the water column above in the drain pipe and 0 psig in the vent pipe. Why wouldn't the water rise in the vent pipe to the same elevation as in the tub so that the pressure in the vent pipe and drain pipe, where they meet, is equal?

After all, the LONG drain pipe offers a lot of resistance to flow whereas the short vent pipe doesn't. And, it takes a good half minute for a tub to drain, so there's plenty of time for the water level in the piping to equalize with that in the tub.



> If it had no vent, the water would "air-lock" and not go down the drainpipe until the fixture was empty and the traps sucked out to let air in. It "would' drain, but very slowly and with heavy bubbling.


OK, how is an unvented bathtub any different than a pail full of water with a hole in the bottom of it? Why wouldn't both drain quickly and with no bubbling whatever?

Why do we need an extra hole (the vent pipe) if not to prevent the p-trap from draining?

All I'm saying is that I can't see why you need more than the drain hole at the bottom of the tub to allow the tub to drain quickly and with no bubbling (or "glugging" as I call it). That draining water will also suck the water out of the p-trap, but that's not the issue here.

You're saying that you need a vent pipe to allow the tub to drain quickly and without "bubbling" or "glugging".

I'm saying that the tub will drain equally well with or without the vent pipe. The only difference is that the vent pipe, being connected just downstream of the p-trap, prevents the water in the p-trap from being sucked out by allowing air into the drain piping behind the draining water whenever the pressure at that drain/vent connection point goes from a positive value to a negative pressure.


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## majakdragon (Sep 16, 2006)

Nestor, sorry I cannot explain all the technical stuff about drains and vents. When i went through my apprenticeship in Ohio, we had a person from the State Code office visit. When we asked how codes were made, he stated that all (drainage) systems were constructed in glass pipe and tested 100 times. If the system failed once, it was against code. This was the same way they tested the theory of horizontal venting. Used to be code that only 20% of venting could be horizontal. After testing, this was changed and as long as it exited the roof, it was withing code standards. As a sidenote, they also proved that flushing coffee grounds down a drain did not "clean" the lines as many people think.


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## Nestor_Kelebay (Jun 17, 2008)

OK, fair enough.

I don't understand all the technical details either.


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