First, in the week after "demo" day, I tackled the scary basement apartment shower room. When we first opened the door, the pervading odor of mold was sickening. We assumed moisture over time, a leaky shower head, and the general dampness of the basement had led to the mold. Once I removed the linoleum flooring, it became obvious that the wall board was completely rotten on the bottom. There was also a nasty patch of black mold behind the radiator.
But only with some more standard plumbing change (yes, the scary little hole in the side of shower wall is the drain into an open basement floor drain on the other side of the wall!).