I noticed the bathroom sink was draining slowly. Our 12-year-old likes to get muddy and then we soak her clothes in that sink, so I thought maybe it was just a bit of mud or debris. But no...
I took out the stopper and had a look -- the inside of the drain pipe was coated with a thick, awful black sludge.
I wiped away as much of it as I could, then I got under the sink and undid the curved pvc trap pipe, and it was also coated with the stuff, although not as badly. It also extended up into the exit pipe, and I cleared away as much of that as I could.
Is this normal? Surely not. Do I need to call a plumber to investigate further?