View Full Version : Basement toilet bubbling up

05-09-2011, 11:59 AM

I can't figure out this problem. I'm attaching a few pictures 1)diagram of my plumbing system 2) picture of the main stack leaving the house 3) picture of the main stack in the basement.

Previous owners installed a half bath in the basement. Toilet bubbles up whenever the 2nd floor toilet is flushed. It only happens when the 2nd floor toilet is flushed. The basement toilet does not get backed up and flushes fine.

I can't figure out if it is a partially clogged drain from the house to the street or just bad designed from the people who installed it. (I guess it could be a combination of both) My guess is, the large amount of water from a toilet flush is just too much for the "T" section at the bottom of the stack and the air pressure is getting pushed into the down stairs toilet.

There is only one vent and that is the vent stack itself. I wonder if a new vent situated on the opposite side of the "T" from the main drain would alleviate the problem. Running a new vent from the basement all the way out the roof would be a nightmare project.

I wonder if venting IS the problem, could I create some kind of loop vent that ties back into the main stack somewhere along it's horizontal.

Please help, I don't know where to start.





05-09-2011, 12:07 PM
The water coming down the stack is forcing air into the toilet bowl.
There should be a vent between the toilet and the stack.
An AAV won't help here. That only helps with suction, not pressure.

05-09-2011, 12:09 PM
So, is there any way to vent this back to the main stack, along its horizontal? Or do I need a new vent that goes all the way to the roof by itself?

05-09-2011, 12:43 PM
While many older houses are plumbed like yours, that no longer meets code. Once a pipe becomes a waste verses a vent, it can no longer be used as a vent for things below it. now, if the pipe is big enough, it often works, but after stuff falls that two stories, the velocity is pretty good, and the basement is showing the worst symptoms. It's likely the stuff on the first floor is exhibiting it, but to a lesser extent.

No, you don't need a new penetration through the roof, but to do it right, you need a vent run that goes at least 6" above the flood plane of the highest drain or 42", whichever is higher. Normally, that would be the sink on the second floor, and often, the best place to tie into the existing vent would be in the attic rather than running another pipe through the roof. The run doesn't have to be straight, but it must have slope to it so stuff like condensation, rain, etc., can drain and not accumulate and plug it up. You may be able to go up to the attic next to an air duct, or some other feature through an interior wall. If you're lucky, you may have a couple of closets that line up on both floors, and you could go through a corner of them.

05-09-2011, 01:15 PM
What if there is no way to get a vent pipe to the highest point of the stack vent without destroying my house? Is there any other options, or should I just leave it like it is?

05-09-2011, 02:04 PM
I would try the STUDOR P.A.P.A. (http://www.studor.net/PdfsForDownload/PAPA_brochure.pdf) (Positive Air Pressure Attenuator)
Provides complete protection against positive and negative pressures in the system.

05-09-2011, 02:20 PM
I would try the STUDOR P.A.P.A. (Positive Air Pressure Attenuator)
Provides complete protection against positive and negative pressures in the system.

NOT TRUE! An air admittance valve only lets air in. This situation requires a path for air OUT. If the AAV let air out, it would let sewer gasses out, which is not good. They do do that when they eventually fail, though.

A loop vent won't do anything for you (from what I know) in this situation. This is one situation where you'd really have to be there to figure it out. You'd need the full layout on all floors to figure out a possible way.

05-09-2011, 03:21 PM
A P.A.P.A. is not an AAV.

05-09-2011, 05:42 PM
You must have a septic tank or house trap in the line, assuming it is not partially plugged, otherwise the air would have been pushed past the tollet without affecting it. If you are going to use an A.P.A.P.A. you might just as well put an open pipe for a vent, since it is going to open to suck air in, and also open to let air out, which an open pipe can also do.

05-09-2011, 07:05 PM
Ugh. Still no straight forward answer. I look at P.A.P.A a bit, but couldn't really see how it works. I can't imagine that it actually lets sewer gases escape, there has to be a trick to it. hj - I'm thinking that when the rush from the toilet hits that "T" section, the flow wants to go both directions which is causing the push out on the basement toilet.

If you look at the diagram I posted, I don't see why I can't tap a vent back into the main stack along the horizontal in the basement. My logic is....by the time the rush from the toilet gets to the "T" section the pipe would be clear on the other end of the basement. Could someone explain why this logic doesn't work?