We were glad to have a separate enclosed head
when we bought Serenade, our 30' sailboat, but the aging toilet system clearly needed some work. The hull had been manufactured with a built-in 27 gallon holding tank in the bow, but the hand pumped toilet mechanism was old and the seals were leaking.
When I opened the inspection port in the top of the holding tank, I could see that the inside was very clean and looked like it had probably never been used. At that time I had the thought that this tank could also double as an adjustable, motorized water ballast system for maintaining the longitudinal boat trim - hmm, 27 gallons x 10 lbs/gal = 270 lbs of extra weight to keep the bow down when a lot of people are in the cockpit ...
I decided to eliminate the hand pump and install an electric pumping system as I already had a fairly expensive macerator pump on hand that I had never used (cost was about $200); it chops the the solid waste into small particles as it pumps.
The toilet itself was in good shape; it is really just a bowl with a water inlet that distributes the flow of incoming flush water from around the inside rim of the bowl to keep it clean, and a larger outlet at the bottom of the bowl to remove the septic waste material.
So I hack-sawed the hand pump off the toilet, which left a protruding pipe end that was perfect for fitting a large diameter 1 1/2" evacuation hose between the toilet and the pump. It also exposed the smaller 1" inlet pipe, since the hand pump is really a double chambered device that pumps water in and extracts the waste at the same time. I removed all the old plastic piping and the seized Y valve so that I could put a new system in place, since the idea of having even the smallest leak didn't appeal to me.
This diagram shows the waste evacuation side of the system that uses the 12 volt high capacity macerator pump.
The y-valve at the toilet bowl outlet can be switched to pump out the toilet or the holding tank. The output of the macerator pump can be diverted to either the holding tank or the through hull exhaust port. The y-valves can also be configured to circulate the holding tank contents in a closed loop through the macerator pump if you want to reduce the waste material to a very fine particulate suspension, prior to pump out.
Note how the thru-hull line loops high above the waterline; this is a very important aspect of the system design because it prevents the sea water from siphoning back into the toilet, causing an overflow onto the floor if any additional weight or heel moves the top of the toilet bowl below the waterline. It is also extremely important to inspect your through hull fittings on a regular basis for any signs of failure. There's nothing worse than arriving at your boat to find that the cabin top is barely visible about two feet below the surface.
These diagrams were drawn with right angle bends in the tubing, but they are in reality smooth curved bends that minimize the friction losses as the liquid passes through.
The holding tank can also be evacuated by a shore based pump-out system, although we never use it in this area because the city sewage just gets pumped back into the ocean in one concentrated spot. We wait until we are out in open water to evacuate our tank, but we will certainly use the harbour pump-out facility if our city fathers ever decide to establish a proper sewage waste composting system, as has been done in the city of Portland, Oregon for decades.
The inlet pump draws fresh sea water from a submerged hull fitting and passes it through a y valve where it can be directed to either fill the toilet bowl or the holding tank.
I made a shower spray fitting in the top of the holding tank so that the inside walls are rinsed when the tank is filled. This allows allows me to fill the tank with water for ballast purposes, as previously mentioned.
Note how the toilet bowl inlet line loops well up over the waterline to prevent backfilling. The check valve at the top of the loop breaks any siphoning action by allowing air into the line when the pump is off. There is also a shut-off valve at the toilet, just to be absolutely sure.
The 12 volt pumps, especially the macerator, draw a fair amount of current (up to 20 amps), so I put an extra bank of deep cycle batteries close by under the V-berth to minimize current losses, and I made sure I used extra heavy gauge wire. All my heavy draw appliances (stereo, subwoofer amp, fireplace fan, refrigerator, anchor winch) are at that end of the boat, so it made a lot of sense to add this extra battery capacity up forward.
There are 2 momentary contact push button switches in the bathroom; one to fill the bowl, and one to flush it. I also installed a sealed Plexiglas inspection window on the top of the holding tank and concealed bypass switches on the pumps that can remain on as I monitor the filling and draining cycles of the tank. Later, I will install non-intrusive FET sensors that will be tied into our Navitrol
system to monitor tank levels.
The system works well, although I may later add an extra, different pump to evacuate the toilet because the macerator pump sounds like the wail of the banshee at 6 am, and is quite loud. When our cockpit is loaded with friends and family, I'm finding that filling the holding tank for ballast puposes definitely allows us to sail closer into the wind when close hauled.