Plumbing and permits are funny. We used to have a little old rental house that we found, did work on before closing (splitting an extra bedroom off the living room), closed on, and had tenants in in eight days. No permit, nothing structural changed, requisite windows in place. Very proud of that project. Anyway, about a year later we got a call from the tenants - they had been at the coast and when they came home there was - stuff - that had overflowed the toilet. Turned out that decades before a family built our place for their son and his family next to the original house - and had "Y"ed into the original house's main sewer line. If the main plugged up below the Y and one house was pushing water to try and clear their drain it would eventually overflow into the neighboring house. Once that was discovered the neighbors and I became best friends and whenever there was a drain issue we would clear it in tandem. We did install individual drain lines later, using a shared ditch to the street when the city was doing roadwork and it became inexpensive.
When we redid our house I got busted with a track hoe digging for a new main drain, two dump trucks in the alley, and our office with about three feet of clear air under it. I'd sent the foundation out for cleaning? Inspector said he had been trying to turn a blind eye, but the activities were a bit excessive. Expensive permits, but mainly a PITA trying to make progress on my schedule rather than waiting for the different boards to meet, inspector to arrive, that kind of thing.
Semantics were involved: we wanted a big freestanding garage, pottery studio, rental storage building. Didn't have the required setback room from the alley without having the garage unattractively close to the house. Tried for about three years to get a garage prmit without success until one day the city planner asked what we were doing with the building. Told him and boom - appurtenant structure permit was approved, and of course we could park cars in an appurtenant structure!
Edit: OP, unless you have a condo with common shared drains in a "wet wall" (back to back baths or shared kitchen walls) you have zero worries. Modern freestanding homes = no worries, all drain connections would be made in the neighbor's house and won't affect you at all.
