Sewer pipes are usually placed at as low a slope as possible, and need at least 2 feet per second velocity to “self-clean” at a given rate of flow. Being a non-pressure system, either a steeper pipe slope or a higher flow are needed to move things along and prevent clogging.
If the new toilets produce a lower flow per flush, then velocity drops below 2 fps in the main, and things pile up in the pipe until enough flow develops to flush things through...
“If the new toilets produce a lower flow per flush, then velocity drops below 2 fps in the main, and things pile up in the pipe until enough flow develops to flush things through...”
Toilets are a very minor portion of the water in a sewer...sinks, dishwashers, washing machines, etc....etc..