New Basement Toilet Bubbles Up When Upstairs Toilet Is Flushed

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blue hill

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Hi folks,
New member here.
We recently renovated our basement and added a bathroom. Now I notice that whenever the upstairs toilet is flushed, the basement toilet bubbles up (air) and it bubbles up quite violently if you flush the upstairs toilet several times in a row. The water in the basement shower drain P-trap moves, but not significantly. The toilets are not connected to a common vent, the basement toilet stack is vented with an AAV in the joist space.
Both toilets are American Standard Champions but purchased several years apart.
Thanks in advance for your help.
 
Your upstairs toilet lacks venting and is pushing on the downstairs bathroom
 
I am not a plumber but I will take a stab at this. I had a similar problem with a friend's house that I was asked to help with.


Your upstairs American Standard Champion creates a powerful flush. When flushed it pushes air that wants to vent out.

Unfortunately the Oatey Sure Vent (AAV) is a check valve and will only allow air into the system. It will not allow the air to vent out.

So it's pressurizing your basement bathroom fixtures.

To test this you can remove the AAV and see if it corrects the problem. I believe it will.

If it does you will have to eliminate the AAV and take that vent to the atmosphere.
 
I am not a plumber but I will take a stab at this. I had a similar problem with a friend's house that I was asked to help with.


Your upstairs American Standard Champion creates a powerful flush. When flushed it pushes air that wants to vent out.

Unfortunately the Oatey Sure Vent (AAV) is a check valve and will only allow air into the system. It will not allow the air to vent out.

So it's pressurizing your basement bathroom fixtures.

To test this you can remove the AAV and see if it corrects the problem. I believe it will.

If it does you will have to eliminate the AAV and take that vent to the atmosphere.

Thanks for the reply gagecalman!
I think you are likely right. I removed the AAV and the problem appeared to go away, but I don't understand why it was fine for about a month and now (with the AAV in place) it seems to be getting progressively worse. Any thoughts?
 
If it only occurs when the upstairs toilet is flushed the the upstairs toilet is the problem that aav is for the basement the upstairs bathroom should have its own vent
 
Yes but if there were no fixture downstream from your upstairs toilet there would be no way to tell untill now with the new bathroom

Well I guess I can't rule out that my vent stack isn't plugged without going up on the roof, but it's worked well since 1959. Your idea would make sense though.
 
Yes but if there were no fixture downstream from your upstairs toilet there would be no way to tell untill now with the new bathroom
Hi Violetl, the upstairs toilet has its own vent to atmosphere and there was a downstairs toilet previously for many years, almost directly underneath the existing upstairs toilet with no problems. I'm also confused as to why the problem is getting progressively worse. We went a month without any issues and this problem has just showed up in the past few days.
 
can you tie in to the vent tat goes thru the roof
Nothing's impossible, but it's going to be quite difficult. Since yesterday, I ran a garden hose for close to an hour and pushed as much water as I could through the downstairs toilet and out to the sewer. I watched the water the whole time through the clean out port on my back water valve and the level never rose at all. Then I closed the port and with the basement AAV removed, I had the upstairs toilet flushed half a dozen times without incident (which is what I expected) then I replaced the AAV and had the upstairs toilet flushed another half dozen times without incident. So I'm led to believe that there was something restricting the flow in the sewer, not enough to back up water, but enough to make the gulp of air go towards the downstairs toilet instead of out to the sewer. My plan now is to run a 2" vent line up into my attic and over to tee into the main vent stack, so I won't have to punch a hole through the roof. I have found that I can have 120 feet of 2" vent, and a third of that can be horizontal. I think I can make that work.
 
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