How were 200 year old houses in America retrofitted for indoor plumbing?

Question:

Answers:
Not easily, if you mean how are they NOW retrofitted. A lot of times the 4" vent lines are sent up through closet space, or the beadboard walls are torn down and the work done between the studs, then drywalled over. Putting in new water lines is much easier now that plumbers are using "flex" piping rather than PVC, CPVC and copper.