Every boat is set up a little differently; Now or Never did a good summary. Here is Selene's setup:
1. When the breaker is turned on, yes, and the pump runs until pressure is attained. My system includes an accumulator tank (or pressure tank). I always turn the breaker off when not in use (e,g, overnight), after one night when one of the old fittings failed and the pressure pump started draining my freshwater into the bilge!
2. I have 2 tanks. There is a valve for each tank, and a further valve for the foot pump. My foot pump draws from the 2 freshwater tanks.
There are three valves under the sink; the two freshwater tank valves - above the valves, these two lines come together into a single line, which divides into two again - one to a further valve and then on to the foot pump, the second aft across to the starboard side to the pressure pump/accumulator system.
3. The water heater fills when the water pressure breaker is turned on. I always run the hot tap a few minutes to purge the system of air, Never turn on the water heater switch when the pressure water breaker is off, or you will burn out the element. I do not have no shut-off valve for the water heater. On Selene the engine coolant is cycled through the hot water heater, which is a great idea as after a day of motoring I have plentiful hot water.
4. The big box mid-salon on my boat sounds like the pullout sink and shower sump. Water drains from the shower/sink into this "box". There is a funky switch next to the head which pumps it overboard (the pump is on the stbd side neat the mast, head throughhulls, etc). As I recall it has three hoses going in to it: One for the shower drain, one for the sink, and one to the pump (then overboard)
FWIW, I have now set up Selene with two bilge pumps, a working pump at the bottom of the bilge, and an emergency pump (using a float switch) just aft of the shower sump. It does make the bilge area rather full of hoses, which can be confusing:
- Engine raw water intake (with shutoff)
- Manual bilge pump hose
- Working Electric bilge pump hose
- Emergency electric bilge pump hose
Good luck!