(Like this.)

I guess the weight of 15″ of water in the top portion of the pipe is enough to push water through the trap. Not sure why the trap is there, though. I always thought traps like that were to prevent odor.

When the freon in the system gets low, the coil in your furnace can ‘freeze up’ (yup - the coil becomes encased in a big chunk of ice!). When that ice melts, the water sometimes runs to exit points that it wouldn’t normally drain to - depends on your coil installation. (Ask me how I know this…) This may be the source of your extra water dripping.
Only way to know for sure is to remove the access panel for the coil.

You can tell if your coil is froze over by feeling the air coming out one of the vents with the system running; the air will be cold, but the flow will be very low.

Good luck. Save some Jim Beam for after the job.

There’s a copper pipe sticking out of the collection pan and it had a good deal of gunk in it, so I cleared it. Still water dripping onto the furnace, but the A/C isn’t on, so I figure it must be left over from when the drain pan overflowed.

Good advice about the bleach, though. I’ll do that when I get home tonight.

Is it common for there to be a gooseneck in the drain pipe? The PVC pipe that goes to the drain has a gooseneck in it about 15″ down from the drain pan.

Disconnect the condensation drain pipe from the collection pan, and dump that Jim Beam down the pipe. What comes out the other end will look very similar to what would exit your cake hole the morning after drinking that bottle of Jim Beam.

Seriously - you might have to ’snake’ the drain line. Then dump some bleach down the line to kill whatever’s growing in there. Get in the habit of flushing the drain line with bleach at least once a year.