I accidentally poured some mortar and grout down my bathroom drain when I was cleaning the remains of a bucket of mortar after tiling the kitchen. The drain was plugged up pretty bad so I tried to scrape some of it out with a wire hanger down the overflow, and that got it flowing again, but its still draining kind of slow.
It's an old house, so the drain isn't PVC, it's galvanized, or bronze, or whatever they used back in the 50's