Our kitchen sink has a stub of pipe which tee's up after the trap about 3 inches higher. There is some sort of device screwed into the stub. I don't see a vent pipe anywhere. I think the device has failed...under sink smells putrid!
Is this device some sort of vent check valve? Lets air in but keeps gases in as well?
I agree that it is probably an AAV. These are "mechanical" in nature, since they do allow air in, but not out. They can fail, but replacing is easy and quick. The Studor brand is about $23 at Lowes. They do sell a metal one also, for a cheaper price, but over time, I think the Studor will be a better value.
If you have never made a mistake, you haven't done much.
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