Yesterday was the third time I'd tried plunging the bathroom sink and having zero effect, so I decided to remove the P-trap (S-trap?) and clean it. After opening the cabinet doors, an idea struck me: am I allowed to do that? I then looked, and it seems the house has shifted and loosened the pipe, which meant there was a very minor leak under the sink so I decided to simply call the property manager and let the professionals take care of it.
The plumber came over at about 10:30, and apparently the slow draining is caused by the grate in the bottom of the plughole. I was skeptical (but kept it to myself) of course, but he removed the grate and it did indeed significantly speed up the draining process. I don't really understand why plunging would speed things up, but I'm not a plumber so I'm satisfied with his explanation. He fixed the leak and went on his way.
Yesterday I also notified the property manager that one of the exterior blinds is making it's way off the house, so they're supposed to be coming around to fix that as well, but as yet no one's showed up.