Head Plumbing

The plumbing circuit for the head will be straight forward with piping runs and valving kept to a minimum. I will sketch the plumbing circuits before I start buying the materials but first I will describe the system one component and/or line at a time.

The holding tank will have a 12 gallon capacity and will be installed on the port side of the sail locker high up on the hull and as far forward as possible. The top of the tank will be just below the main deck but with enough space to accomodate PVC fittings for pump out, inlet and two vent  lines. The bottom of the side hull tank will be above the waterline thereby satisfying the anti-siphon requirement on the discharge side. The two vent lines will be located on opposite ends of the tank and vent to the outside on port and starboard sides.
The Lavac head will be tied to a to a Henderson hand pump on the sea water intake side. The top of the Lavac head will be above the water line but I will still incorporate a vented loop into the line. The manual henderson pump will be mounted on the sail locker side of the bulkhead roughly even with the top of the hoding tank.  The keyed whale discharge pump contol and the ball valve that isolates the tank and whale pump will be mounted on the same bulkhead. 

The holding tank discharge line will run from the bottom of the tank to the discharge seacock valve. When at sea the discharge seacock valve can be left open so the flush routes to the holding tank and gravity feeds straight thru and out the boat. In harbor the seacock valve is closed.

The pump out line will be a separate line from a pick up tube at the bottom of the tank running straight up to top deck through hull.

So holding tank up high with four lines: vent, on deck pump out, manual pump fill and gravity discharge. Now.......will it work? and to steal a line from "Marathon Man", "is it safe?".

I'll attempt to answer my own questions. Relying only on gravity for the tank discharge system is asking for a clogged line. But this is easily solved by installing an electric pump for the overboard discharge. but now that there is a pump in the discharge line you will need a tank shut off valve so that the holding tank contents do not sit on the top of the pump or drain thru the pump to the closed seacock valve below. In port then, the tank shut off and seacock valves are both closed. To empty the tank at sea, open both valves and kick the pump on. Once the tank is empty and rinsed close both valves. In principle it's best that the seacock valve be normally closed anyway.


Is it safe? I think so; as long as you have the tank above the water line there is no need for a vented loop on the discharge line side.

Some sail locker storage space is lost with the tank mounted in the sail locker on the port side but you pick up chain storage space under the sail locker deck. Even with the addition of the discharge pump and the tank shut off valve the circuit is still pretty short and simple. From start to end it goes, seacock intake, toilet, flush valve (Henderson bilge),tank discharge line shut off valve, discharge pump and discharge seacock valve. Of course the system includes an independent vent line and an independent pump out line. The lines will be a combination of PVC and hose.