On Feb 3, 5:17 pm, Richard J Kinch wrote:
That is a shallow trap. Certainly not of legal dimensions for a sanitary
drain. The workmanship of the plumbing overall isn't encouraging.
I'm trying to figure out if there's a way to somehow intentionally
empty the trap so I can see if the smell comes without having to run
the kitchen sink.

Plumb in a trap with rubber Fernco couplers. This lets you open it up for
testing and blowout.

A plumber told me there wasn't enough elevation to put in a deeper
trap, though he said I could have one put in the wall if I had to, so
might try that.

But while I can understand how pressure differences caused when the
kitchen sink runs could suck water out of thep-trap, I don't
understand:

a) how this connects to the condensate line, as I thought those were
separate from any line the kitchen sink would connect to, or

Your condensate drain is connected to the house sanitary drains, right?

Are they usually? I know very little about plumbing.

You may also have a venting problem on your house drains.

How can I figure out if that's the problem? There's a vent pipe over
my kitchen on the roof but I have no idea how to tell if there's a
problem with it.

Thanks for the help, by the way!