Winterisation of Marine Toilets

Proper winterisation of marine toilets is extremely important and is essential to save mess, money and masses of work which may be caused by the damage inflicted on plumbing and toilet mechanisms by freezing, so, a few generalisations to start.

It’s a little difficult to separate toilets from the plumbing generally. The higher pipes and fittings are at most risk over winter, those installed lower benefit from the above freezing temperature in the water underneath the boat.

When considering holding tanks, it is almost unheard of for water to freeze in any way that will damage these unless the tank is filled to the point where water is in the tank vent. There is a school of thought that maintains it is better to leave the freshwater tank nearly filled to maintain its cleanliness.  If you would rather drain the tank, ideally close the breather in some way, but be sure it is opened before re-commissioning the system.

WARNING: Do not use normal vehicle antifreeze in a domestic plumbing system, it is poisonous. 

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Winterising your Toilet:

First, you will need to establish if the toilet flushing water is provided from the boat’s freshwater system or from the outside flotation water.

Typical method for treating systems flushed with flotation water.

In these cases winterization of the toilet is entirely separate from winterising the boat’s domestic water system.

Close the inlet seacock and disconnect the hose from it.  

Make sure to re-connect this hose before re-opening the seacock.

Make up a mixture of anti-scale solution. This can be vinegar based or a proprietary product such as LeeScale.

Draw this solution through the system by pumping the toilet. Leave in system for 24 hours. Block the pipe to contain the solution.

Next, flush this solution out of system with a strong mixture of water and soft washing up liquid.

Now drain the system where possible following the guidelines for your type of toilet shown later in this article. Reconnect the hose to the seacock and leave with sea cocks closed.

Typical method for treating systems flushed with onboard fresh water

Lee FreezeMake up a mixture of anti-scale solution such as LeeScale. Flush the toilet system thoroughly by pouring this solution into the bowl and flushing. Leave the solution in system for 48+ hours. (No danger if left longer)

Then disconnect the inlet hose at the domestic fresh water pump and replace this with a short hose drawing from a container of anti-freeze solution. Allow this to go through the entire plumbing system by opening each tap and operating the toilet. This negates the need to drain the system.

WARNING: This solution must be a product specifically supplied for freshwater domestic systems such as LeeFreeze and thoroughly flushed through again with freshwater at re-commissioning.

When flushing any marine “domestic” system with anti-freeze, pour a solution of water and soft washing up liquid into the toilet bowl and flush through with the anti-freeze solution. This will protect the valves and other rubber components.

Draining different types of toilets: (only required if not anti-freezing the system)

Chemical type:

Chemical toilet

Not much to do with these, make sure they are completely empty, give them a good washing out, dry them thoroughly and perhaps put a small amount of a “fragrant” chemical in the tank to guard against smells. Depending on age and use, (the toilet not the owner!) some chemical toilets have replacement service parts and these should be replaced if they have been malfunctioning or leaking.





Macerator type - Sanimarin

Macerator type toilet

Turn off water supply.

Remove water supply pipe (in this case by pulling from porcelain as shown)

(For other macerator toilets check manufacturer’s instructions)

Hold this pipe over a container at floor level to drain water.

Operate the toilet to open the valve and allow all residual water to drain out.


Dump through type - Traveller

Dump through type toilet

(This toilet is sometimes called a Mansfield and is similar, for winterisation purposes, to the foot operated Vacuflush)

Note: Pedal cover removed for clarity!

Turn off water supply.

Put a shallow tray or cloth underneath the foot pedal.

Remove water pipe by unscrewing from the bottom of the foot pedal mechanism as shown.

Depress foot pedal to empty fresh water.

Hand pump type - Jabsco

Hand pump toilet

Operate the hand pump in “dry bowl” mode to empty bowl as much as possible.

Then close seacock to turn off water supply.

Put a cloth under the drain plug at the base of the toilet to catch residual water.

Remove the drain plug as shown by turning quarter of a turn anti-clockwise.

Operate the pump again to clear any remaining water


Electric Vacuflush type - Dometic

Electric vacuflush type toilet

Turn off water.

Disconnect inlet water hose from supply and hold over a shallow container at floor level to drain.

Operate toilet to fully empty water.

Note: after working on any of the above toilets make certain that all pipes are re-connected. Don’t forget to turn water supply back on before use.

General notes:

Rubber components and seals etc in marine toilets and pumps benefit from not being left dry. A simple way to ensure this is to occasionally flush with a soapy solution.

Over winter ensure that the water pump is switched off.

Check all hose connections for leaks.

Check and tighten all hose clips.

This is also a great time to consider fitting a service kit, new seals or to replace any worn pipes or hoses.

Please remember that just because a hose is “white” it isn’t necessarily Sanitation Grade. Poor quality or non Sanitation Grade hose will almost certainly result in smells permeating through the hose walls.


Leesan sticker

Anyone who contacts Lee Sanitation and asks for a sticker will be sent one FREE!

For further advice on winterising your toilet system check the LeeSan web site