Sewage and the sea

John Champion delves into murky territory when he boldly goes where few cruisers would go if given a choice.

Our cruising homes, like land-based ones, require toilet facilities that can reasonably be expected to work when needed. Unlike shore-based plumbing, marine versions are not supported by a legion of on-call professionals 24 hours a day, with significant infrastructure and a host of standards designed to ensure minimum levels of compliance and functionality. More likely you will be your plumber, system designer and technician in this less than glorious but essential area. More likely you will be your plumber, system designer and technician in this less than glorious but essential area.



This is perhaps the place to start, and there are many models available to choose from. If you are buying a new boat the choice is probably made for you unless there are options available.

If buying second-hand, the choice is certainly made. The first choice is manual or electric flush. Both have advantages but newer boats will usually have electric models. These have the significant advantage of initial maceration (grinding waste into small pieces), which is required by law in Queensland and many other states and countries before discharge overboard. This function also allows a greater variety of holding tank options.

Electric toilets have a couple of disadvantages: firstly they are electric and must be installed in what is traditionally a wet area with the obvious potential problems. More expensive models may have a sealed or remote motor to minimise this potential. They use power to operate, which means no juice, no flush and electrical misers may resent the power consumption but bear in mind a 10-amp draw for 30 seconds is less than one-tenth of an amphour so nothing to get really twisted about.

Of greater concern is the potential for blockage. Electric toilets of the economical varieties (OK cheaper) frequently employ a smaller-bore discharge line. This is as a consequence of the macerator function, the logic being the stuff is ground into smaller particles and so needs less space to be transferred to a holding tank or overboard. This is true, of course, but it is also true that a smaller pipe is more vulnerable to – ah how shall we say – “foreign objects,” foreign objects being anything other than a recent meal and small amounts of toilet paper.

Usually the macerator process is noisy – imagine running a blender at 0300 and you have the picture. There are numerous flasher models that are quiet but expect to pay much more for these units and I have heard “extortionate” and less polite words used to describe the spare parts. Increasingly popular with new boats is the Vacuflush system, which utilises an electric-powered vacuum pump to flush the toilet and uses fresh water to do so. Fresh water use is far less conducive to odour production but better super-size that water-maker, stock up on parts and bone up on vacuum technology before heading off on that cruise.

Manual toilets naturally have to be pumped clear. Some people don't like this and cheaper ones are seldom up for the long haul. Whatever you buy, make sure it is big enough for people over three years of age, securely fastened and strong. Vented loops are required in all below-waterline installations; these will stop your boat flooding if a siphon is established through either the intake or discharge lines. Some people like to close the seacocks when not in use anyway, and if there are no vented loops you better.


Down the line

The toilet is the first step of what may be a long voyage. If offshore, then overboard discharge is legal and is the best possible solution. From my experience the contents of a holding tank are seldom a precious cargo and the less time it spends aboard the happier we remain. Trouble with a holding tank is big trouble.

So we have two basic options here, assuming we are also going to comply with no- discharge legislation, and both require a holding tank. A Y-valve can be used to divert the “product” either directly overboard or to the tank. If we have an electric toilet, there is potential to mount a gravity-drain holding tank.

This is arguably (and I'm sure there will be argument) the simplest and hence the best solution. All the dunny contents pass through the macerator and are pumped up into the holding tank, which is mounted above the waterline of the vessel, preferably at maximum heel. The tank will ideally have a funnel or inverted pyramid-shaped base to encourage maximum drainage. This base is connected to the largest-diameter hose possible and in as straight a run as possible leads directly to the largest practical thoughhull fitting.

When the seacock is open direct discharge is a matter of course (well gravity) – close the seacock and the holding tank is in operation. Include a deck pump-out fitting (assuming there is an operational pump-out facility available in your hemisphere) and you have a simple, effective, fully functioned legal system.

But sometimes this just ain't good enough; I recently saw a new production yacht fitted with a gravity-drain tank with a Y-valve for direct discharge to a second through-hull! Knock another hole below the waterline, add another join in the pipe, trust an additional fitting and rely on extra hose clamps to achieve an identical result. An effective gravity drain tank requires a relatively high position, which may mean sacrificing a hanging locker or other valuable space. This is preferably close to the toilet because hose runs are best kept short.

Below-water-level tanks will require a pump to discharge overboard. If the toilets are manual this one will have to macerate as well and macerating pumps will burn out if run dry. This means a momentary switch (only operates when it is pressed, release and the pump stops) is favoured by the smart money.

Electric diaphragm pumps have no such compunctions, so timers are possible, hit the switch and go and do something else but to comply with regulations the product has to have passed into the tank via a macerating toilet. Same for manual holding tank pumps, which are serviceable, reliable and affordable but increasingly rare as technology dependence becomes a more integral part of our lives.

If the holding tank has a single outlet, both the shore and sea pump-out options will need to share this outlet. This requires a Y-valve to select the desired destination. Add the other Y-valve for overboard/tank selection and this increasingly complicated (yet workable and legal) system has numerous joins that is avoided with the gravity-drain system. Easy to see why many manufacturers embrace gravity-drain systems.


Storing the unspeakable

Black-water tanks, as they are politely referred to, are largely all that is between us and a serious onboard incident. For this reason economy and frugality are our natural enemies when choosing a system. Get the best possible or carry some sort of hazardous materials suit and 100L of Dettol. Most people working with holding tanks reckon that high-density polyethylene is the best stuff and the thicker the walls the better. All holding tanks require an inlet, outlet, vent, deck pump-out (if your vessel supports this) and ideally a large, secure inspection port. The finest tank in the world will only be as good as the hoses and clamps used. Proper sanitation hose is strong, durable and hideously expensive. It should be smooth-bored so less likely to trap the merchandise and must be highly odour-resistant.

Use cheaper stuff and it may not leak (for a while), but it will make itself known. Hose clamps are also between you and the fertiliser, so use two and the non-perforated types will chew up the hose far less. Features such as rotating fittings for these hoses will help installation.

All tanks must be vented to the outside of the vessel to prevent collapse and our black-water beauty is no exception. Imagine connecting up the pump-out station and promptly imploding the tank; enough to put you off the feed for a while. The vent also allows air at the precious cargo, which promotes bacterial growth (with the addition of additives) that helps alleviate the perfume previously known as “Oh God that stinks!” Speaking of vents, if the tank is overfilled then this becomes the logical route as more water and such is pumped in, existing contents are forced up and overboard via the vent. This is bad. Firstly we are discharging in no-discharge zones, painting the side of our vessel with crap and probably blocking the vent in the process. Block the vent and implosion returns to our horoscope.

Retrofitting holding tanks, especially on smaller or older vessels where the designer could never even imagine such a concept, may well have you researching worm farms.


Measuring the unspeakable

So you have a holding tank and it is the best of its kind; you have a direct-discharge option, deck pumpout and discharge-at-sea option. All components are premium, correctly installed, accessible and maintained.

Very good, but how much is in the damn thing?

A sight gauge here is for dedicated weir dos. There are many monitors and alarms available these days to let us know just how much cargo we are packing. One of the dumbest has a green light for OK and a red light for full. Another has a thing that goes beep (loudly) when full; bit late then if you're settled in for the night. Other systems give a percentage readout on a digital monitor, which is more helpful, but I have not yet encountered a system that seems to work for very long. Relying on an instrument whose accuracy cannot be ascertained is dubious policy. Most of these devices read through the tank walls (couldn't expect them to work inside), and it seems as product adheres to tank walls the sensors are confused. Would you trust a depth-sounder that was intermittent?

Solution: get rid of the cargo as soon and as frequently as possible. More sophisticated treatment systems will allow a little more flexibility in discharge locations but most are still illegal in many of the places we want to sail. Funny (not ha ha) that the end product is often better than the municipal variety that is joyfully pumped into the sea.


Managing the cargo

I heard once that the only useless spare part on the boat was the service kit for the dunny because if you wait for the thing to fail before installing it, well too late. The idea was to regularly replace the serviceable items so as to prevent any problems. Makes good sense because it will only break down when required to work, and you know what that means.

Some toilets have parts kits priced almost out of this world. For a very small amount more a whole new unit can be purchased and in some cases it may be quicker to simply replace the whole unit. This is a terrible waste of resources, of course, so price and availability of parts might be required before deciding your throne of choice.

A common and inevitable problem with salt-water flushing units is calcification of the lines. This insidious phenomenon will gradually but surely reduce the interior diameter of the discharge line with the accumulation of salt particles.

Eventually there will be no room for cargo to pass and bingo, that's when the screaming starts. Vinegar, as we all know, will slow the process but if calcification is already present then will probably be next to useless. Stronger acid may help but new hose will really do the job. Salt water stinks over time (short time) if left to lie in hoses so flush the lot thoroughly, leave it full of vinegar and do your snout a favour.

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