As you can see, I have a 16 gallon water holding tank to the right, a 2.8 gpm Sureflow 12 volt pump to the left, and kitchen sink drain and incoming water supply in the center. I ran two 3 wire + ground 14 gauge cable down the same hole as the incoming water supply hole to connect a solar charge controller (next photo) and the other to an inverter (not shown). One of the cables is attached to an outside water proof two plug outlet, one for the solar panels and the other to attach the battery to the controller. the other cable is to attach the inverter to the battery which will be located outside. I know it sounds odd to use standard ac plugs to run my 12 volt system, but a plug is a plug is a plug. (I hope :) Also, I plan on adding a switch box to change between on grid and off grid power supply. That will be situated between the incoming supplies and the breaker box.
Back to the water. As I see it... The red port on top of the water tank will be for a 3/4" water supply line and maybe a manual supply port. The one directly below it will be outgoing to the little pump. The blue one on top can be for venting and the other bottom one could be used for a manual drain port. I'll give it more thought :). I ran 3/4" pvc schedule 40 underneath the trailer then I reduced to 3/4" PEX to complete the supply. I'll use 1/2" PEX to run the supply to and from the pump to the sink, shower and hot water heater. I didn't elbow up through the floor, I used a T which I adapted to half inch PEX which I will run to the toilet.