As a home owner builder, we may do our own plumbing and electrics etc. The bulk of the rough services are put below the floor – so check and double check and test the installation before putting in the floor.
Go to your local suppliers and they will probably give you lots of advice. The building inspector would like to see a job well done too.
The rough plumbing (laying down the sewage pipes and hot and cold water lines) can be done before the first inspection.
Sewer pipes (assuming you have a septic tank) are 3 inch diameter and must have a minimum of 2% slope to the septic tank.
Make sure you have a clean-out extending to the outside of the dome.
If you are in a free building zone you may want to consider building your own septic tank from earth bags. Stucco cement the inside. Go on-line for specs. It would be dead easy to do and cheaper than buying one.
The Health department made us have a septic pump-out from an existing tank that has been in use for 12 years now. ($ 210 down the drain so to speak). They “recommend” a septic pump-out every 3 years. (Job security?) So the guy comes over and said it was the nicest pump-out he has ever seen. (like it’s his “high” for the year LOL) We told him that we are vegetarian and do not use chemicals to wash with or clean with. No big-M’s there.
Try drain as much clean water to nature. Perhaps routing only toilet and grey water from the kitchen sink to the septic. Septic tanks are biodegradable machines and do not ever require pump-outs if you treat them with care. We thought of requesting a composting toilet – but one step at a time hey?
Pressure test your sewer line by filling full of water with a 5 foot static head. They had better not leak?