Recently noticed the thread asking about a wash-down pump. I did install one several years ago and it is a great convenience in our cruising area where most of the better anchorages are mud bottom.
Because I had converted the toilet to fresh water I had the sea-cock available that had previously been used for the head intake. The pump is mounted in the far forward section of the cabinet on the port side just aft of the head. The wash-down hose is run alongside the cold water hose that services the head. There was not sufficient room to run the new supply hose to the bilge, so there is a notch cut in the fiberglass immediately aft of the head to accommodate that hose. The notch is not visible when the mattress is aboard. The wash-down hose is mounted on the port side of the chain locker coiled in a section of Schedule 40 PVC pipe. Below are photos of the hose coiled in and the hose pulled out so you can see the outlet for the hose to be attached. I did have a spare circuit because I had replaced the original breaker panel, so the pump has a stand-alone breaker. The sea-cock is open and the breaker on only while pulling anchor.
It seems to me that if you were using seawater in the head, a Y-Valve could be installed to route the water to the pump only when you are pulling anchor.