So I decided to pull the p-trap out from under the sink in the master bath, because it had been draining very slowly. It was the old style chromed steel drain, and there was some corrosion at the fittings. Long story short, I ended up having to sawzall the drain pipe apart, and run to the store to get a new (PVC) trap. And you wouldn't believe the mess I found in there.....
Suffice it to say I know now why you don't see plumbers chewing their fingernails. I'm glad I know enough to do little home repairs like this, but some of these are just.......ugh.