AAV failure with septic pump-out and related questions

[Rossn]

I had my septic tank (3 chamber with lift station) pumped last week, and that evening, after my wife took a shower, the master suite filled with septic gas (might have been some present before). After 1/2 hr of scratching my head, I remembered a Studor Mini Vent in the closet, behind the clothing. it is on a drain that serves the shower and one lav. Former owner remodeled this area in 2005, so I assume the AAV is around 20 years old.

While currently under another remodel, my daughter also has her bedroom in the walk-in closet, so immediate safety issue comes to mind.

A few questions:
- Is it more likely that the AAV failed due to suction while being pumped out (maybe they hit the inlet) or pressure building in the empty tank as the shower ran?
- I am not confident venting is setup correctly, or sufficient. What is the best way to test the current roof vent is functioning correctly? Tissue over the top while flushing or running water down it?
- What are the requirements around venting of main lines serving a septic tank?
- For safety reasons, would it be reasonable for the next 4 months (while my daughter is in the room with the AAV) that it is plugged, when serving only a shower and lav?
- Who makes the highest quality AAVs (least failures)?

 

[Reach4]

Is it more likely that the AAV failed due to suction while being pumped out (maybe they hit the inlet) or pressure building in the empty tank as the shower ran?

Of those two, I guess the second one sounds better to me.

Did you try blowing through the failed unit as a test?

For safety reasons, would it be reasonable for the next 4 months (while my daughter is in the room with the AAV) that it is plugged, when serving only a shower and lav?

I don't think there is much of a safety issue.

Who makes the highest quality AAVs (least failures)?

Studor is the originator. I don't know how reliability compares.

 

[Sponsor]

 

[Jeff H Young]

Im not confident the house is vented correctly either and not every one or even all codes think AAV has a place in plumbing but not to worry Id stick with a major plumbing brand like oatey , soux chief , studor and replace the valve or just simply remove it see if its stuck wash it out or whatever see if it works and replace coulda been extreme pressures positive or negative and it just stuck open somehow also could be a open pipe or crack in piping somewhere went un noticed without the extra pressures of the pump out

 

[SepticTankMan]

Septic guy here -- seen this exact scenario more than once. A few things:

The pump-out almost certainly finished off that AAV rather than causing the whole problem by itself. A 20-year-old Studor is well past its service life -- the diaphragm gets brittle and either sticks shut or hangs open. The strong suction during pumping (and then positive pressure as the empty tank refills while the shower runs) is exactly the kind of event that kills a tired AAV. So: age was the loaded gun, the pump-out pulled the trigger.

One important technical point: an AAV only lets air IN (relieves negative pressure). It does nothing for positive pressure. So if tank pressure was pushing gas upward, even a brand-new AAV wouldn't have stopped it -- that's the roof vent's job. Which brings me to your test idea: yes, the tissue test works. Hold tissue over the roof vent while someone flushes; it should tug inward slightly. Better yet, run a hose down the vent from the roof -- if water backs up, you've got a blockage. Bird nests and ice dams are the usual suspects.

Do NOT plug that AAV for four months. An unvented shower and lav will drain slowly, gurgle, and can siphon the trap dry -- and a dry trap lets in far more sewer gas than a working AAV ever would. These are a cheap part and a five-minute swap. With your daughter sleeping in that closet, just replace it this weekend. Studor, Oatey Sure-Vent, and Sioux Chief are all solid; honestly they're comparable these days, the bigger factor is replacing them proactively every 10 years or so when they're inside living space.

And since there's a kid involved: septic gas isn't just smelly, hydrogen sulfide is genuinely nasty at higher concentrations. New AAV plus confirming the roof vent is clear, plus pouring water into any floor drains or traps that may have dried out, and you'll be in good shape.