Good point. I also heard (from a fairly credible source) that most plumbers in the area simply won't touch units in a particular large old condo building here,

Good point. I also heard (from a fairly credible source) that most plumbers in the area simply won't touch units in a particular large old condo building here, because it's just not worth the headache or liability of dealing with the building condition and quirks. It sounded like the reason wasn't just the usual skilled trades preferences for kinds of work (e.g., new construction), but rather, yet another unpleasant surprise of old rotting apartment buildings.