Finished the demo part of the bathroom remodel to find pretty significant damage to the floor joists caused by the original builder's "design" (see photos/video). Setting aside how I'm going to fix or at least mitigate the damage - what would have been the correct way to plumb in the toilet and sink drains without weakening the structure?
Given the small floor joists, I can't imagine the right way to try to drain across them this way. So what would a pro builder have done to install this bathroom correctly?
More context: This is the 2nd floor of a 2-story, 1920s house. This bathroom and its stack are directly above the 1st-story bathroom. The stack is perfectly vertical from the basement to the attic, where it has a slight offset to exit the roof. The existing stack is cast iron and all existing drains are steel/iron.
The toilet drain pipe in the wall drains both upper and lower commodes before Y-ing into the main stack 5' above the basement floor.