The Whale twist shower is unique in that the hose is actually TWO hoses in one and the mixing valve is in the faucet handle (head) itself. Because I needed two pumps, one cold and one hot, I found the Mini Jabsco units that add up to more GPM and less $ than a single big Jabsco demand pump. It works very very well.
I now wish I had moved the pumps elsewhere to allow more room behind the panel for the hose to drop in.
I did some interesting things on the heater as well. The return hose from the core to the engine goes into a Y connection on the suck side of the S/w pump. The heater Co wants like 45$ for their fitting. Mercruiser has it for for 3.87$ I have the part number if needed.
The whole idea of this mod was to add a heater and hot / cold shower and not loose any significant storage. Not easy but done.