Basement Toilet Bubbles When Upstairs Toilet is Flushed

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PstrSteve70

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Problem: My basement toilet bubbles or gurgles when the upstairs toilet is flushed but not all this time. This started AFTER a bathroom remodel.

Background: I have been in my 44 y/o house for 15 years with no problem. I discovered during the renovation that the bathroom sink was essentially venting into the wall and not to the pipe stack that goes through the roof. They apparently used a AAV - Air Admittance Valve. The contractor also noticed that the pipe coming out of the ground was not capped on the Y joint (not sure I'm using the right term) so he capped it off. You can tell where the white PVC meets the off-white pipe. This was completely open. Had no idea this was the possible source of smells over the years. In the attached picture there is an AAV covered in blue bag to keep out dust during construction. The blue bag was removed before the wall was finished. The contractor also relocated the sink plumbing to the adjacent wall. Once the bathroom was finished and the sink installed, we started having problems immediately. Within 4-6 hours of the sink being installed, we had a full-fledge sewer backup. Paid a plumber $350 to snake it from the front yard. Problem solved or so I thought. The next day, the toilet started gurgling with the upstairs toilet was flushed. Thinking the AAV was bad, I cut the wall open in the adjoining room and had the AAV replaced. Is there anything else I can do to stop this toilet from gurgling. Busting up the floor or tearing through walls is not an options as I spent over $6000 on this bathroom already. As long as the sewer doesn't back up I can live with it, but it is annoying and I'm always worried about a backup. BTW, the basement shower, toilet, and sink all drain fine. See attached picture.

AAV.jpg
 
When you had the full backup I'm assuming sewage was in basement and plumber cleared a main line blockage?
 
Lots of wrong in one photo. I'm assuming it wasn't a real plumber who installed your bathroom

- 180 degrees of change on your trap arm before your vent is not allowed
**edit** I see now you say he moved it.
- You cannot use a wye when connecting a trap arm to a vent

- you cannot wet vent a toilet off 1 1/2" pipe, or an air admittance valve. The toilet in the basement is bubbling because when you flush upstairs, there's no vent to absorb the sudden positive pressure in the drainage system, air will escape through where ever it can...in your case, the lower level toilet. This will also prevent your system from draining properly, leaving you more susceptible to blockages.
 
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When you had the full backup I'm assuming sewage was in basement and plumber cleared a main line blockage?

It was mostly black crud looking stuff that came up out of the floor drain. He rain the snake through the access in the front yard until the clog was cleared. Did the sink plumbing cause the backup? I've had sinks backup before, but never had to have the main line snaked in 15 years.
 
Lots of wrong in one photo. I'm assuming it wasn't a real plumber who installed your bathroom

- 180 degrees of change on your trap arm before your vent is not allowed
**edit** I see now you say he moved it.
- You cannot use a wye when connecting a trap arm to a vent

- you cannot wet vent a toilet off 1 1/2" pipe, or an air admittance valve. The toilet in the basement is bubbling because when you flush upstairs, there's no vent to absorb the sudden positive pressure in the drainage system, air will escape through where ever it can...in your case, the lower level toilet. This will also prevent your system from draining properly, leaving you more susceptible to blockages.

Matt, the contractor used a subcontractor for the plumbing I don't have a before picture to know what it looked like. I came downstairs and they had already begun re-routing the plumbing. I had to assume they knew what they were doing as I'm not a plumber. Why would a contractor or plumber suggest rerouting plumbing without knowing the ramifications or to ensure proper venting? The bathroom wall is a half wall of tile, so I can't destroy the wall. The plumbing you see is accessible on outer walls, if I call a REAL plumbing contractor, can this be vented properly and fixed?
 
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