I bought and rehabbed a 2-flat in chicago this year and now I'm turning my attention to the basement. It was a legal 3-flat but the last owner had it decoverted to storage a year before the sale. I was told there was a plumbing problem in the basement and a clean out had to be installed.
When the last owner had it converted to storage, the took out the bathroom/kitchen plumbing and electrical. They even poured concrete in the toilet and shower drain.