Also, it is the norm for all water that goes down drains in houses to go to sewer. Someone mentioned about septic tanks and using the laundry sink... So whether you flush down the toilet or wash down the laundry sink, kitchen sink, shower, etc, it will end up in the sewer. The issues I see are introducing germs and causing clogs. But rinsing newborn poo down the laundry sink should be fine.
That was me we have absolutely no town connections out here well except for electricity and phones but yeah for people on town supply dunny is the best place for baby poo's. we need to clean everything fairly frequently because of our water so not too worried about germs etc either.