Sea water flush:
Pressing a button on the control panel in the bathrooms activates a dedicated electric pump, which draws sea water from a through-hull seacock, through a filter and into the toilet bowl.
Manual toilets are the same, except sea water is sucked in by operating the toilet’s hand pump.
Fresh water flush:
After physically changing over the valve and pump connections the actual flushing operation is the same as for sea water, except the fresh water pump now pumps water into the bowl, or it comes in pressurized through the dock supply. In the case of a manual head, fresh water is drawn in with the manual pump.
First I tested the one-way check valves by connecting it to a dock water hose, which is about 65psi. In it’s flow direction there was no restriction, but when connected to the opposite end of the check valve absolutely no water came out.
I then tapped into the boats cold water pressure pipework and installed the solenoid, the shut-off valve and one-way check valve. Then I joined them into the pipe feeding the toilets, using a tee connector. Note that the manual ball valve is the one connected to the toilet pipe, then comes the one way valve, then the solenoid. This arangement ensures that no sea water can ever get to the solenoid or percolate back into the fresh water 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 coming from the toilet control boxes in each bathroom previously activated the dedicated sea water inlet pumps. I fitted the positive wire with quick-change connectors on the pump and solenoid wires so they can be quickly and easily changed over. The two negatives, (returns), from the pump and solenoid go to ground. I did consider doing this operation using a double pole, double throw switch mounted remotely somewhere, but since it is necessary to physically open and close the ball shut-off valves to change the flushing method, I decided it was just as easy to switch the pump and solenoid over at the same time. This also meant one less switch to go wrong, and it’s not as though I change the system frequently.
In the case of manually operated toilets it is just necessary to connect the solenoid to a 12 volt supply, through a switch near the toilet. When the switch is activated the solenoid opens and permits fresh water to be drawn into the bowl using the hand pump on the toilet, and when switched off the solenoid closes again. This wire can be permanently connected to the solenoid.
That’s the installation, it’s actually easier to do than to describe it.
To obtain a fresh water supply, I (1) close the sea water inlet sea-cock, (2) connect the positive wire from the control box to the solenoid positive wire. (3) open the fresh water supply ball valve shut-off.
Of course, if the boat is piped into a pressurized shore water supply then it is unnecessary to connect the boats pressure pump.
(Also, on manually operated toilets operation (2) is not needed, because the switch to the solenoid is already connected).
At this point the solenoid is closed and along with the one way check valve prevents any sea water already in the pipes passing into the fresh water system.
When the control panel button is operated, (or the switch in the case of a manual head), the solenoid instantly opens and the water pump pressurizes fresh water into the bowl, exactly the same as if a faucet had 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 closes.
To switch back to sea water flush the process is reversed. (1) The fresh water ball valve shut-off is closed (2). The electrical wire from the solenoid is changed over to the sea water pump. (3) The sea water sea-cock is opened.
Fresh water flushing has a major secondary advantage, but which will only be seen as a benefit when it comes time to dismantle the head to install new parts or replace the pipes, (which it surely will—as certain as the wind is always on the nose). You will no longer need an oxygen apparatus to do the job.
I consider fresh water flushing to be a major improvement to a very necessary, but often unmentionable, piece of my boats equipment.