Both Britannia’s heads are Raritan “Elegance” electric models that were one of the first things I installed, to replace the horrid little hand operated heads that constantly leaked. They have performed flawlessly thus far, principally because for about 90% percent of the time they are flushed with clean freshwater.

The corrosiveness of seawater is well known to sailors and the filthy brackish water in the Intracoastal Waterway does not help either. Even “clear to the bottom” seawater conditions do not prevent calcification of the pipes and valves, or its frequent offensive odor. It isn't so much human waste that causes the foul stink commonly emitted from marine heads, but seawater born micro-organisms that die in the pipes and are then pumped into the bowl, usually on the first flushes after a period of non-use.

Flushing marine heads with freshwater prevents these problems and most manufacturers recommend seawater flush toilets should be flushed with freshwater occasionally, especially when leaving the boat for any length of time. This also prevents that nasty brown ring in the bottom of the bowl.

My new heads were raw seawater models, but I then devised a modification that allows them to be easily interchangeable between freshwater and seawater flush. Raritan offers a kit that converts a raw-water flush toilet into freshwater flush at the press of a button but it does not have the one way check valve or a shut off valve like my system. The factory system is also specific to the Elegance head, whereas my method will work with any marine head, whether electric or manually operated. This is because it is fitted on the incoming pipework, not in the actual body of the toilet like Raritan’s. Their kit costs $190 and my equipment is $80

My objective was to be able to flush the toilets with freshwater from either a marina shore water supply, or the boats freshwater tanks, and to ensure the freshwater system is totally protected, both automatically and manually, from any incursion of seawater when converting back from freshwater to seawater, and vise versa.

I achieved this by using a 12-volt stainless steel water solenoid valve, that is normally closed and watertight by default and only opens when current is applied to it. Not wishing to rely entirely on this mechanical/electrical device to prevent back flushing I also incorporated a manually operated ball shut-off valve, along with a one-way check valve as a third protection. All this is in addition to closing the seawater seacock before changing to freshwater flush.

Like most boats of her size Britannia has an on-demand electric pump, drawing from her freshwater tanks and pressurizing the boats complete water system. Basically I interconnected this supply to each of my two heads, so when the solenoid valve is activated the toilet flushes with freshwater. The method can also be used to flush manually operated heads with freshwater, even if the boat does not have a pressurized system.

When in a marina I usually connect to the pressurized dock-water supply with a water hose to a pressure reducing regulator in the boat. I can then switch the electric pressure pump off and have constant silent water pressure throughout the boat, including the heads. I have also incorporated an automatic solenoid shut off to this water inlet in case of an internal pipe failure.

Even when under way I normally leave both heads on freshwater flush, especially in the ICW and short passages elsewhere. But then Britannia has a very large potable water capacity of 325 US gallons, and it will depend on the capacity of your freshwater tanks and the number of people using the heads whether you change over to seawater when on a passage.

A urine flush uses about a quarter of a gallon of water in Britannia’s heads, and a full flush about three quarters of a gallon.
                                                            seawater OPERATION:

Pressing a button on the control panel in the bathroom activates a dedicated raw water diaphragm pump that draws seawater from a seacock, through a filter and into the toilet bowl. Manual toilets are the same except seawater is sucked in by operating the toilets hand pump.

                                                           freshwater FLUSHING:

After physically changing the valve and pump connections the actual flushing operation is the same for freshwater as it is for seawater, except the boats freshwater pressure pump now pumps water into the bowl, (or it comes in pressurized through the dock supply when in port). In the case of a manual head, freshwater is sucked in with the toilet manual pump instead of seawater.

                                                                                                  INSTALLATION.

This is easier to actually install than it is to describe. There are three components.

A plastic one way check valve and a regular ball shut-off valve can be bought from most hardware stores. I bought the 12-volt solenoid from Amazon.com., who also have a 24-volt version.

First I tested the one-way check valve by connecting it to a dock water hose. In its flow direction water flowed without restriction, but when connected to the opposite end of the check valve absolutely no water came out. That's how it should be.

I then connected the parts together into an in-line assembly consisting of the solenoid, the shut off valve and the one way check valve. Then I connected them using tee connectors between the boats cold water system and the seawater inlet pipe that feeds each toilet. You can see in the picture that the manual ball valve is connected next to the toilet pipe, then there is the one way valve, then the solenoid. This arrangement ensures that when in raw water flush mode no seawater can ever get to the solenoid and never percolate back into the freshwater system. The installation is under an easy to reach floor board. Interconnecting the pipes would be just the same for a manually operated toilet.

A 12-volt wire comes from the toilets control boxes and normally activates the seawater inlet pumps. I fitted this with quick-change connectors on the pump and solenoid wires. When in seawater flush mode the wire is connected to the seawater inlet pump, but when using freshwater the wire is changed over to the solenoid. The two negatives (returns), from the pump and solenoid go to ground. I actually considered making this wiring connection using a double pole, double throw switch, (like what Raritan uses), mounted somewhere near the toilets. But since my system has the added safety of the manual ball shut-off valve it is necessary to physically open and close this valve to change the flushing method. I therefore decided it was just as easy to switch the pump and solenoid power over at the same time, and with one less switch to go wrong, and it's not as though we change the flushing method frequently.

In the case of manually operated toilets it is only necessary to connect the solenoid to a straightforward 12-volt supply, through a switch near the toilet that can be permanently connected to the solenoid since there is no pump on a manual head. When the valves are turned to freshwater and the switch is activated the solenoid opens and permits freshwater to be drawn into the bowl using the hand pump on the toilet. When switched off the solenoid closes again.

                                                                                                                       OPERATION:

To change over from seawater to a freshwater flush. (1) First the seawater inlet seacock is closed, (2) the wire from the seawater pressure pump in changed over to the solenoid. (3) the freshwater supply ball valve is opened.

On manually operated toilets operation (2) is not needed because there is no pressure pump and the switch to the solenoid can be permanently connected.

When the control panel button is operated, (or a switch in the case of a manual head), the solenoid instantly opens and the water pump (or shore water pressure), pumps freshwater into the bowl, exactly the same as if a washbasin faucet has been opened. It takes only a few seconds to fill the bowl and when the button is released the solenoid closes and the water stops.

A manual toilet would be pumped by hand, and after flushing the switch would be returned to ‘off’ and the solenoid closed.

To switch back to seawater flush the process is reversed. (1) The freshwater shutoff is closed (2), the electrical wire from the solenoid is changed over to the seawater pump, (3) the seawater seacock is opened.

freshwater flushing has a great secondary advantage, but which will only be appreciated when it comes time to dismantle the head to install new parts or replace pipes, (that is as certain as the wind is always on the nose). You will no longer need an oxygen apparatus to do the job!

I consider freshwater flushing to be a major improvement to a very necessary, but often neglected, (until a problem occurs), piece of my boats equipment.