Any idea what this pipe is under my kitchen sink? I think it must be the main A/C drain line. We don't have any under our bathroom sinks so I'm thinking they combined all 3 A/C units and ran it to the kitchen. Any thoughts?

Also, see my other thread regarding replacement of this sink. I assume there's no reason I need to keep it entirely pvc and can use typical black hose with clamp so it can be removed if needed? Right now it's fully glued which I think is partially because it was a weird angle.

https://imgur.com/a/hwgrawR

Hmm ok then will need to glue back together when done.

Definitely the vent for the sink.

Your drain/vent is usually hard piped like it is. All the piping for the trap up to the sink can be taken apart by unscrewing the compression fitting and disassembling.
You would go back in with the same type of set up. The fittings have some adjustment built in.

Diddler_44 said:

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It's an improper vent, FYI.

Should be at least 6" above the flood rim of the fixture before turning horizontal.

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That does raise a question, What kind of location is this sink in? On a peninsula or why is the drain coming up the middle of a the cabinet and the vent out the sidewall?

It is in a peninsula so I suspect they have the vent running over to the column before turning vertical (incorrectly as pointed out).

Any ideas on my options for a solution? I'm no plumbing expert, it seems like possibly an AAV is an option but even then still might not be code?

Yes. Just go straight up out of the top of the tee and put a studor vent as high as you can.

You can then just cut out whatever horizontal pipe that you can get to and cap the other end in the attic.

You probably have a window above your sink which is why the vent isn't able to go into the wall and on up.

Is there any negative to only capping the pipe under the sink and just leaving the vent open through the roof? My only concern is I don't know if anything else might be venting through the same pipe.