Toilet installed on rough in - venting issue?

[corewo]

Hello all.

I am finishing up a bathroom in our basement and we were "lucky" to have a rough in already in place. According to blueprints it was 3 pipes. 1 for shower with built in trap, 1 toilet, and 1 sink.

We did not add a shower so that one is capped and unused. We added a toilet and a sink. On the sink line we included an AAV based on local inspectors suggestion as a need. We have one other tub sink in the basement that was original that had an AAV on it.

So we installed the toilet and sink and the sink works good. But the toilet will not flush well. It goes down but very very slowly.

To test I did a few things.
1. removed the AAV on the sink next to toilet.
RESULT: The toilet flushes well, but I hear ALOT of bubbles and air movement in the opening where the AAV would be.
2. put the AAV back on.
RESULT: the first flush or two will work, but I get air and water movement in the SINK next to the toilet. From that point on, the flushing is back to minimal slow drain only.

I believe I have a positive pressure problem? Everything I was told was a wet vent like I installed would work. But it is obviously not.

Any ideas what I can try next? There are no other known issues with plumbing in the house. Here are pictures of the rough in before work, and the AAV installation. Last is a video of what it sounds like when the AAV is removed and the toilet is flushed.

Thanks for any tips. (I have called a plumber for arrival next week, but I am trying to see if I can get to the root myself before then)

 

[corewo]

Here is the aav.

 

[ReelPlumber]

When the toilet is flushed the water entering the drain is causing a positive pressure in the pipe. The AAV is not allowing the displacement of air to escape causing an air lock. Once the water gets passed the vent the AAV now allows the water to suck air in so the water can continue down the pipe.
In the past when we have come across this issue, we have had some luck by extending the vent as high as you can get it and increasing the pipe size. Doing this will allow for more air to be displaced and let the system breathe a little better.

 

[Jeff Handy]

Sounds like the main drain line is partially blocked.
Could be from construction debris in there, or roots, or a sag in the line.
A normal vent allows air in and out.
Your AAV only allows air in.
A partially blocked drain can cause slow flushing because the flushed water totally fills the drain pipe, and has to push lots of air ahead of itself.
Air that would normally have escaped up a vent pipe.
When you pull off the AAV, there is probably trapped air pushing out of that connection during a flush, check that out.
The drain water from the sink is slower and less volume, so the drain pipe can maintain an air space ahead of the draining water.
You could have the drain lines camera inspected all the way to the street.
And any clogs cleaned at that time.
If there is a partial clog, it will probably get worse as the toilet is used more.

 

[Twowaxhack]

You probably have a pipe obstruction.

 

[Jeff Handy]

You probably have a pipe obstruction.

Haha, that’s what I said, in my usual long-winded version.

 

[corewo]

Thank you all. I cannot extend this AAV due to its location under the sink and alignment with the wall. Hopefully the plumber Monday can camera down there and see if something else was up. I am just confused if it’s a blockage how we have never had back up issues elsewhere? It definitely seems to be positive pressure but I am at a loss on how to fix that having no way for a normal vent.

 

[Twowaxhack]

Thank you all. I cannot extend this AAV due to its location under the sink and alignment with the wall. Hopefully the plumber Monday can camera down there and see if something else was up. I am just confused if it’s a blockage how we have never had back up issues elsewhere? It definitely seems to be positive pressure but I am at a loss on how to fix that having no way for a normal vent.

Obstructed pipes cause positive pressure when they start filling up with water and there’s no vent to relieve itself.

 

[breplum]

Remove that cap on the shower and see what happens.

 

[Twowaxhack]

Unless you’re flushing into a sealed tank or drum......or there’s a big belly in the pipe holding water, it’s not a venting issue.

 

[corewo]

Update:

After more testing and different things here is where I am and what I have done.

1. The toilet now flushes well and consistently with the AAV on. However, it bubbles HEAVILY in the sink next to the toilet that the AAV is off of. Sometimes it doesn't at all, and other times its a lot and even water comes out of the drain a bit in a sputter. Definitely still air trying to escape but only on large flushes.
2. I removed the clean out cap in the main in the next room that comes from upstairs. It enters into the cement and I believe it feeds into the same main line under the slab. Removing this has NO effect on the issue. The air bubbling in the sink continues.
3. Down the line I have another sink that has an AAV. I removed this AAV and had again no effect on the issue.
4. I have one of those cheap Amazon camera line things so I stuck it down the toilet hole. I can only get to about 3 or 4 feet before it loses its ability to be controlled and I saw nothing but open pipe. Very clean with just a tiny river of flowing water at the bottom.

If it was positive pressure, wouldn't opening the 4" clean out fix that? Or even the other AAV down the way? That would suggest if there was an obstruction it would be after my new toilet, but before these insertion points. Right?

If it matters I am on city sewer.

I have a plumber coming tomorrow to put all this to rest, but I am stubborn and like to figure things out. I also am not excited about the cost to probably get this video'd and snaked without knowing for sure it will show anything. I am hopeful for an honest plumber.

Thanks again for the tips everyone.

 

[corewo]

Unless you’re flushing into a sealed tank or drum......or there’s a big belly in the pipe holding water, it’s not a venting issue.

City sewer so no sealed tank. If its not a venting issue, what else could it be?

 

[corewo]

Remove that cap on the shower and see what happens.

I removed the cap a while ago in testing. Because its a shower there is a built in trap with water so it had no effect on air escaping. Its behind a wall so I would have to get someone else to flush so I could watch for air bubbles.

 

[Twowaxhack]

City sewer so no sealed tank. If its not a venting issue, what else could it be?

An obstructed drain line or a belly in the pipe holding water.

 

[corewo]

Hey all I wanted to update on what the root cause ended up being. The plumber came today and the first thing we looked at was the sewer cap. While I was spending my time using the clean out access, he right away assumed the problem would be there. He explained there is a flapper installed there and it would make sense if it was broken, or stuck. Sure enough, about 3 feet after the toilet/sink hit the flapper was siliconed! The builders when they roughed this in were missing 1 back flow cap. Instead of getting one they siliconed a temporary plastic cap on and left it. The issue is the silicone was put on so thick it dripped down and enclosed the hinge part of the flapper inside. So while water could pass through, not enough causing my issue. We removed the flapper, and all the excess silicone. Put the flapper back in and voila. FIXED.

Here is the cap, spot/flapper and the silicone we removed. Thanks builders! Never assume because something is roughed in by professionals that everything was done right....Lesson learned. Now I am on a search for a proper 4 inch back flow cap to screw on here.

 

[Twowaxhack]

Yep, drain obstruction.

 

[Jeff Handy]

Maybe that piece was glued in to test the sewer drain for inspection, then forgotten about and not removed as was planned?

 

[corewo]

Maybe that piece was glued in to test the sewer drain for inspection, then forgotten about and not removed as was planned?

Probably.

 

[arctic bill]

AAV are fine to relive negative pressure, however before a toilet can flush it has to push air out of the way. a vent would do this but not a AAV.