I'm reasonably close to doing plumbing, and I have some down time doing Army training to just sit and think.
Basically, I have two 30-gallon fresh water tanks and a 50-gallon grey-water tank under the master bed in the back of the bus over my rear engine. Also under the master bed will be the hot water heater, filters, water softener, accumulator tank, water pump, various valves, pressure gauge, etc.
Off of this, I'm running to a washer/dryer and a sink on the passenger side, plus a sprayer of some kind by the front door. On the driver side, I'll run an indoor and an outdoor shower, plus I'll have my water inlet, dump valve, and a spigot (to drain). I'll need to use sump pumps on the drains because the gray tank is inside the bus (the one under the shower will need to be under the floor and heavily insulated). I also have plans for a recirculation pump for the hot water.
I'm still working through what to use for a sprayer by the driver door, an outdoor shower, gravity fill/overflow/air vent, and dump valve. Most of the RV stuff has great reviews, but when you get your hands on it , it's made of flimsy plastic that looks like garbage and wouldn't last long. I'm also still trying to figure out how I want to do cut-off valves and trying to make sure I can properly winterize.