About a year ago I replaced the old manual head with a new electric head. I plumbed it with fresh water fill/flush but wanted to add a sea water option. The fresh water option will be used whenever there is easy access and abundant water. When sailing offshore or cruising in areas where fresh water isn’t easily available, the head would be switched over to using sea water.

I added a 1:2 valve, a Jabsco pump (taken from the old refrigeration system), and T’d into the sea water input for an easy project that was accomplished in a weekend. Here is a drawing of the project showing the new plumbing inside the yellow boundary. The green lines represent sea water and the blue lines fresh water. The sea water pump is wired to the electric head control board so when the fill button is pressed, the pump will activate. A disconnect switch was added to open the wiring to the sea water pump when the system is in fresh water mode.