Bog Standards – A Guide to Boat Toilets


Get any group of boaters together and it won’t be long until the conversation turns to toilets.  This is meant most literally as boaters discuss the myriad of toilet types available and their inherent maintenance issues.  Whether ordering a new boat or browsing for second hand vessels there are several choices to be made when considering a loo.

Pump-out or cassette?

Boat toilets are not like regular land toilets.  By their very nature boat toilets cannot be fed directly into the sewers and will need to store their contents for disposal at some later time.  This invariably means a second encounter with your bodily waste and so it is worth considering which toilet system you prefer. Your choice of toilet typically comes down to two options – Pump out or Cassette.   Cassette toilets have a small removable unit in the base where waste is collected and stored.  Pump-out toilets rely on a larger immovable storage (or “black water”) tank, often located beneath a bed or integrally in the bathroom.

Cassette Toilets

Cassette toilets are the most popular option for boaters and there are several reasons for this.  Firstly they are often the cheapest to install with basic models costing around £70.  These will usually be plastic construction with smaller volume cassettes and water reservoirs, and have lever or plunger pump flush systems.  Whilst units in this price range are entirely functional there are more luxurious models available with features such as electric flush and larger cassette options.  The purchase price is not the only saving to consider when you choose a cassette toilet.  Emptying the contents of your cassette into a sanitary disposal point is usually free whereas there is almost always a charge to pump out a black water tank.

Another important benefit of a cassette toilet lies in the ease with which they can be emptied.   A pump out toilet needs to be taken to a pump out facility in order that it may be emptied.  Sometimes this is not possible; for example if you have broken down or if the weather prevents you from moving your boat.  If your tank is full and you are nowhere near a pump out facility then you are in deep doo doo!  Thankfully, with a cassette toilet you can always take Mohammed to the mountain.  Removing the cassette for emptying at the nearest facility is much more convenient if your boat is immobile for any reason.  Many boaters also keep spare cassettes, just in case they are caught short.

On the downside, cassette toilets are sometimes considered a little uncivilised by the uninitiated.  The integral storage unit of cassette toilets means their appearance differs from conventional land loos, leaving guests puzzled and your pan full.   Emptying a cassette is an experience that many find objectionable too, and a full cassette is quite a weighty load to carry if the disposal point is any distance away.  Eroded seals in the unit can also cause problems, although all seals are relatively cheap and easy to replace.  Most cassettes have a ventilation pressure valve which can stick shut if the seal is worn.  This can cause a build up of gas pressure and a vapourous release when the toilet is next used and flushed.  Ageing seals in the cassette can also allow unpleasant leakage.

Pump out toilets.

Those desiring a more conventional looking toilet will often plump for a pump out system.  These look much more like the toilets you would find in a house and this is often reassuring for those new to boating.  Indeed, even some experienced boaters prefer pump out systems, not only for the aesthetic benefits, but because emptying them is much less of a “hands on” experience.  Emptying your black water storage tank means a visit to a pump out facility where there is almost always a charge.  (Usually around £10 – £20.)  Once paid, emptying involves simply affixing the hose to your storage tank outlet and switching on the machine; the contents are then simply sucked from the tank into either a large tanker unit or directly into the sewers.  Many boaters find this to be a much more agreeable process to endure than the emptying of cassettes.  Staff in private marinas will often perform the procedure for you whereas BW provides automated facilities (which are credited using a pre-payment smart card or token) and you perform the task yourself.

Pump out toilet installation costs vary depending on the type of tank and the type of toilet you choose, and there are many variations to choose from.  “Dump through” systems sit atop a black water holding tank which is usually made of steel.  Prices for toilet pans vary from £180 for the basics to £600 for the most regal model.  The pedal flushing systems of most brands are universal across the range and so paying more money for your toilet buys you a pretty pan rather than any increased reliability.

Vacuum and compressed air toilets are becoming increasingly popular as they seal off the waste from view once flushed.  This complete disassociation is an attractive benefit for those who prefer a “home from home” toilet experience.  As with all toilet system benefits there is a price to pay for convenience and these systems are expensive compared with the other available options.  A vacuum loo will cost between £1000 and £1400 for the vacuum generator and pan combined, whereas a compressed air system will knock you back £2000.

As some pump out toilets can be sited apart from their storage tank it is worth considering that the pipe-work has the potential to store up to four flushes worth of waste before it arrives at its destination.  Michael Punter, from Lee Sanitation, recommends a “rise and fall” method to routing waste plumbing.  “The waste hose should rise steeply as it leaves the pan before falling gradually into the top of your black water tank.  A vacuum or compressed air flush will easily push waste over the apex of the pipe. It can then travel downhill at its leisure into the waste tank, thus avoiding it being stored in the pipe-work for any period of time. It’s also a good idea to keep waste pipes away from hot water plumbing in order to avoid drying and blockages.”

Costs and convenience are not the only variables to consider when comparing pump outs with cassettes.  Pump outs are more prone to blocking than their cassette cousins and this can be a monumental problem.  All manner of items can disagree with your pump out toilet and visitors are often the unwitting culprits.  Disposable nappies, sanitary towels, tampons, condoms and moist toilet tissues are amongst the countless objet d’art removed from blocked pump out loos.  It is easier to say what you CAN put into a pump out than to list what you can’t, and the list is only two items long.  The first is anything that has passed through your digestive system, namely faeces and urine.  The second item is common or garden toilet tissue.  Boaters with delicate derrieres should be aware that luxury and quilted toilet tissue does not break down as readily as do the more “value” brands.  Vacuum toilets also have a reputation for being prone to blockages which are usually due to over-enthusiastic tissue usage or plumbing installation problems.

Blockages can also occur when the contents of your tank harden.  This can happen if your tank is left for a period of time or if you forego the use of decomposition fluids. This allows the contents of your tank to dry out, solidify and collect at the bottom.  Quality toilet tissues can exasperate the problem until the lumpy sediment collects and solidifies to such an extent that it cannot be sucked by the pump out machinery.  The tank outlet eventually becomes blocked and remedying the situation can be a truly unpleasant experience. Whilst blockages are rare and mostly avoidable, pump out owners invariably have a story to tell about their toilet tribulations.

There are several ways to address the blockage problem, none of which can be called a joy.  Those with a “dump through” facility can utilise a stick or a length of flexible cable with which to palpitate the blockage, the aim being to break it up to pieces small enough to pump out.  Another method by which to do this is to use a pressure washer, but be sure to take care to avoid any splash-back!  Caustic soda and sulphuric acid can be used as a last resort, but be sure to confer with an expert if you decide to go down this road, particularly if your tank is plastic or has no vent system.

Some pump out toilets have macerator units fitted which grind up any waste before it is stored with a view to negating blockage problems.  Whilst anything which helps avoid a blocked toilet must be applauded one must care to avoid blocking the macerator itself as foreign objects can cause the unit to seize.  Consider also that it is impossible to access black water tanks through a pan with a macerator unit.  Most experts consider a tank with a sealable inspection hatch to be a useful insurance in any pump out set up.

Finally, eroded seals can be a problem with pump out toilets too as water from the pan can leak through faulty seals into the storage tank.  This can quickly fill a black water tank if the flush water is pumped from the main water supply tank.  Again, replacement seals are cheap to buy and although replacing them on a pump out system is a little more work, it is entirely do-able by those with the nose and the inclination.


Storing any amount of bodily waste for any amount of time will generate some smell.  There are several ways of dealing with this problem with the most common remedy being chemical warfare.  There are several brands of chemical liquids available for use in both pump-out and cassette systems, most of which are blue in colour and/or name.  These formaldehyde based fluids can be mixed with the water used to flush or used as a solution added directly into the storage tank  but whether you actually like the resulting chemical smell is a matter of taste and tolerance levels.

Flushing dump through toilets can release the gasses that build up inside sealed black water tanks and the odour can be quite offensive.  This can be negated by fitting a breather hose from the top of your tank, venting directly outside your boat and most new boats are fitted with these as a matter of course.  Breather hoses allow methane to escape gradually from the tank and not build up in the first place. They should be at least equal the diameter of the inlet pipes as this allows equal displacement volumes of air and waste when flushing and pumping out.

Eco-Friendly Toilets

Boat life is often conducted in close synergy with nature and so it is not surprising that chemical free eco friendly toilet systems are becoming increasingly popular.  The simplest way to achieve this is by replacing formaldehyde solutions with the more environmentally friendly nitrate and oxygen based products which essentially speed up the natural de-composition process.     Brewers yeast tablets are also effective in the fight against smells but be aware that the residues left behind by conventional chemicals stop both yeast and nitrate fluid systems from working.  Boaters wishing to make the transition from formaldehyde to more eco friendly options usually purchase a replacement cassette, although a period of abstention from chemical usage and some vigorous rinsing may do the trick.     It is more difficult to rid black water tanks of formaldehyde as they tough to rinse and cleanse effectively.

Composting toilets are becoming more popular on boats too, with a variety of systems being available.  With some care they can be wonderfully effective in avoiding both smells disposal problems.  In a nutshell they work by allowing oxygen to do its job of drying and composting the waste and most utilise sawdust as a means of ensuring desiccation.  Obviously liquids (such as urine or less solid faeces) can cause problems for the drying process and if you don’t dispose of your wee separately then you’ll need to use much more sawdust to keep the compost dry and aerated.  Other systems include a heated or fan-dried composting compartment which helps to evaporate the urine more quickly.  In my view these systems miss the point entirely by using energy to power the units and doing a poor job of composting to boot.

In reality, most composting boaters don’t actually compost their waste on the boat, but transport it ashore to decompose there.  The toilet systems I have seen in use are simple bucket and chuck-it affairs, usually comprising of commode type throne which is emptied to a compost heap ashore.  But many people forget that by forgoing use of the mains sewerage system entirely, composters do not add to the environmental impact of sewerage farms. Along with the reduced chemical impact on the environment, composting toilet owners also save water (by not flushing) and seem to grow the most delicious strawberries.


Many thanks to Michael Punter from Lee Sanitation, Bob Mills from NB Elijah and Darren from NB Dunster for their advice and information.

Box Outs

Sea Toilets

Sea Toilets were popular on boats before it became illegal to dump sewerage directly into the waterways system.  These lever flushing toilets are still available but must now be pumped into a storage tank.  Although some older boats still have overboard pumping sea toilets fitted, the Boat Safety Scheme means that alternative toileting facilities must available.

Water Usage

Toilet Type Average Water per Flush
Dump Through 0.5 – 1.5 Litres
Macerator 2.5 Litres
Vacuum 0.5 – 1.5 Litres
Compressed Air 3 Litres
Lever op Sea Toilet 4 Litres

Top Toilet.

Top of the range vacuum cassette toilets closely resemble a conventional home toilet with a floor standing ceramic bowl, but can cost around £1100

Self pump out equipment

Self pump out kits do exactly what it says on the tin.  The kit is either operated manually using a lever or is powered electrically and pumps out the contents of a black water tank into the disposal points used by cassette owners.  This usually negates the cost of using traditional pump out facilities but is more a hands-on approach.  A few BW disposal facilities (usually septic tank based) are not free for self pump out users as the volumes being discharged are closely managed.

Toilet Tissue.

Recycled toilet tissue is becoming more robust as manufacturers are increasingly using bonding agents.  The guys at Lee Sanitation recommend a simple test to see how appropriate your brand of tissue is for boat loo use.

Put two sheets of toilet tissue into a pint glass of water and stir well.  If the tissue breaks up easily then it is boat approved.  If it stays in sheets then give it a miss!

Breather Hoses.

Most of us do not notice any smell from the breather hoses which vent outside our boats, but if you would like to spare the noses of delicate passers by then you may wish to fit an inline carbon filter.

Toilet Trouble 1. Bob – Leeds Liverpool Canal. West Yorks.

A friend of mine was carrying his full cassette to be emptied one summer afternoon when he slipped and fell on the towpath.  As the cassette hit the floor it burst open, covering him with the contents, which was unpleasant enough.  However, his sympathies lay with the guests on the restaurant boat moored directly next to the incident who were attempting to enjoy an al-fresco lunch.

Toilet Trouble 2. Ruben – Erewash Canal.  Derbyshire.

My parents enjoyed occasional days out on my boat in the summer but my mum was particularly wary of my dump through pump out loo.  They came to visit one weekend and on arrival my mum rushed to use the loo after the long journey from London.    I was a little worried when she called my dad for help and even more so when I found out why.  Somehow my mother had managed to drop her car keys into the pan and flush them into the poo tank.  I was left to retrieve them while they retired to a nearby pub for lunch.

Published Waterways World Magazine – June 2009


~ by Tony's Desk on June 21, 2009.

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