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Home » Product & Planning Guide » Toilets » Pump Out Toilets on
Narrowboats & Canal Boats


Making use of bulk holding tanks and modern "household" style bowl units, pump-out toilets are first choice for many boaters.

Here we offer some thoughts to help you decide if one of these systems is for you.

Pump-Out Toilets
In these systems waste is fed to a holding tank which, depending upon usage and capacity, is regularly discharged into a land based sanitation station, be it tank or mains sewage.
The pump bit of the kit is actually land based so the term refers really to a holding tank system that is pumped out remotely.
Holding tanks can be made of stainless steel but a more common material is polyethylene. Wall thickness should be between 8-10 mm and should be of at least a medium grade.
The pump outs themselves are situated at sanitation stations managed by the Canal & River Trust around the inland waterways network.
Many private marinas and boat yards also operate pump-out facilities. Not all of the CRT sanitation stations have pump-out equipment and guides of the services available in specific locations may be obtained from the CRT on request.
Self Pump-Out Equipment

Some owners of pump-out systems carry their own portable pump-out kit. This enables them to use standard chemical toilet waste disposal points which are much more common than the dedicated pump out facilities. Please be aware if the Elsan disposal unit flows into a tank this needs to be emptied and often you cannot use self pump out kits. If the Elsan flows into the main sewer there is no problem using one. (see direct instructions). Self pump out kits are now available to include a rotating drum for the hose which should make storage easier aboard. Generally the system includes a single action diaphragm pump and is available in manual and 12v or 24v electric versions.  

Macerator Toilets

A macerator is a machine which reduces solids into smaller pieces, think of it like a soup maker!. This means that transfer through pipe work is eased & that the breakdown of waste in the holding tank is accelerated. Latest systems have an inbuilt macerator within the porcelain of the toilet bowl which makes a very simple, space saving and elegant installation.

The smallest macerator on the market currently is only 295mm (11.6in) high, which makes it practical for smaller boats and cruisers.  It is also designed to use minimal amount of water per flush, only 0.5 litres compared to the average 1.5 litres.

There are also macerator toilets on the market with a 360 degree rotating bowl, allowing it to be fitted in to the most restrictive of areas. You do need to be very careful with what is disposed of in a macerator toilet to ensure no blockages occur. The pipework is normally only 1.5 inches wide and it is not unheard of for lipsticks, lighters, baby wipes etc to be found to be the cause of the problem!

Vacuum Flush Toilets

Used in conjunction with a holding tank, these systems have a small vacuum tank and pump installed in-line before the holding tank. The tank itself is of heavy duty construction in line with the specification of the system.

They use very little flush water and are very simple in operation. A vacuum is created in the waste pipe work which sucks the waste in to the pump. Whilst recreating a vacuum for the next flush it will send the waste in to the holding tank. By their nature, the seals and pipe work have to be maintained in tip top condition to prevent air or water leaks.

Even the biggest capacity tanks will require emptying. As we mentioned above, some Canal & River Trust sanitation points have a pump-out station. A large number of marinas on the system also offer pump-out services. At the time of writing this service will cost around £15 per session & some stations will require 2 go’s at getting the tank clean. You also have the option to buy (and store on board somewhere) a range of self pump-out equipment that will enable you to use sanitation points that do not have the facility.

On board tanks also require dosing with treatment in order to assist the breaking down of the waste so this cost has to be factored as well. Some marinas and boat yards will offer this included in the price of pump-out.

It's worth ringing ahead to marinas and boatyards on your route to get an approximation of cost. Use our Products and Services Directory for an up to date list of those yards offering pump-out facilities.

During the first fix, it is important to plan for the system install. It is much easier at this stage to decide on the position of sanitation pipe work and holding tanks than to try and retro-fit when the boat is completed. Not impossible, just easier and less costly.

Considering the ballast weight of a full tank is important. Ideally the tank should be central, but on a narrow boat this is difficult. Theoretically, a tank could be installed centrally if built into the bilges under the sub floor but this would take careful planning of pipe work and regard to future access. A deep bilge would be required to account for top mounted level indicators and vent pipes.
Remember with a waste holding tank all fittings must be taken from the top of the tank.

Practically, the most common location for the holding tank is under the bed base or dinette.

Work out ballast requirements on a half full holding tank for the best compromise and accept that when either empty or full there may be a bit of movement from the horizontal. In practice this will be barely noticeable if you plan well.

At this stage all electrical supply cables and water supply pipe can be planned and installed as well.

Remember to correctly size cables with reference to power requirements and voltage drop.

Don’t forget to reference the inside system components with the exterior deck fittings. Don’t forget to use ISO standard deck fittings or else you will come a cropper when pumping out. Try where possible to minimise pipe work runs to external vents, flush and discharge ports, with an eye on how easy the ports are to access when you actually pump-out. Common locations for deck fittings are in gunnel tops or the centre of the roof. There is a compromise where ever you fit them as sometimes the gunnel will be on the opposite side to the pump out station and it needs a fairly nimble person to use roof mounted ports. Ideally pump out fittings in the stern deck will aid discharge and make the fittings easier and safer to access. This is not always possible but worth thinking about.

The Tank
Decide on the size and position of your holding tank. Blank rotary moulded plastic tanks are a good choice because you can decide on the position of the tank fittings. Good quality polyethylene is the material of choice when using a tank for waste.
Refer to the manufacturer’s recommendations when cutting holes for waste in and pumping waste out.  Cutting holes in a plastic tank is a simple process when using a good quality drill mounted hole saw. Usually all that’s required is ‘waste in’, ‘waste out’, ‘rinse’ (optional), a’ vent’ and finally a ‘level indicator’. It is advisable to cut another access/inspection hatch for ease of future maintenance, nearest to the waste out pipe. It’s easier to sort a pipe blockage if you’ve planned ahead!

Pipe Work
Don’t compromise on the pipe work. Use only the best quality sanitation grade material as recommended by the toilet system manufacturer. Ensure that it is not too difficult to access in the future for replacement so be mindful when mounting clips and fixings. If it won’t be accessible there is always the option to use ABS plastic pipe work and fittings.

Once the holes are drilled and the pipe work connected, test all the electrical connections to any accessories such as tank level indicator and control panel whilst you can still get to the tank.
The vent pipe will vent odours externally through a skin fitting. It is still important to fit an in-line charcoal filter to ensure an odour free cabin. Also worth mentioning, the vent size needs to be the same size as the waste in and waste out. Simple physics!

Make a note in your boat maintenance schedule for planned replacement of this inexpensive charcoal filter. This is often overlooked and owners can get used to and not notice slight internal odours which make an unpleasant environment for visitors. Whilst on the subject of odours, over a number of years, even the best pipe work can become porous to odour. If you have a used boat with issues such as this, replacing pipe work and filters can often revitalise the system and is an alternative to removal and full replacement. A quick test if you suspect the hoses may have deteriorated is to run a damp rag on them and then smell the rag outside of the boat.

Once the tank is in and the pipe work connected, it’s a simple matter of installing the electrical controls for flush, near the loo, and the main control box. Remember to allow for maintenance access to the main control box and to ensure it cannot get contaminated by any future water leaks.
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