I've posted this problem a few times over the past year, but still no
luck. But maybe fourth time's a charm, and I've learned some things
since my last post...

When I run the kitchen sink, and the AC kicks on, I get a bad smell
throughout the apartment. If I run the kitchen sink, and the AC is
off, I get the same smell, just much fainter. I put a cork in the
pipe where it enters the drain pan, and run the kitchen sink and AC,
and got no smell at all. So I'm guessing it's coming from the drain
line. It's of varying strength, and I don't know if it's sewer gas or
not, but it's definitely unpleasant.

I had a plumber open up a wall next to the AC unit. There's a
separate condensate line, and he found where it came out in the bottom
of my building.

While I could possibly understand maybe I'm getting a bad mold smell
off the condensate line, what I don't understand is why it only
happens when I run the kitchen sink.