[l1tany11]

A lot of problems are also due to old systems. Ask any plumber. The plastic pipes are smooth inside. Old pipes weren’t only rough, they degrade. Cast iron sloughs off into itself. There was a kind of pipe that was used that was basically tar paper; it broke down and clogged itself (like cast iron).

A new building with new toilets should work very well. Replacing your toilet may not help if your pipes from the 60s are basically nonexistent.

[mveety]

Orangeburg pipe is the tar paper stuff. It's a time bomb. Not only does it break down with use it also flows (flattens with gravity/overburden pressure, bends over unsupported sections run through walls/floors, etc) over time as well, especially in a hot environment. So even if it doesn't get much use it will collapse and/or stretch and break.

[brnt]

Indoor pipes still can be horizontal for long stretches, where smoothness doesn't help if it's flushed only a few times per day. It also depends on the stool. I never cause obstructions, but my wife on the other hand...