Managing Grey Water

WORDS AND DIAGRAMS BY JOSEPH VAN WOERKOM
PHOTOGRAPHY BY NICK WELSH AND PAUL KLAT

With more and more people becoming attracted to the free-camping lifestyle, most new RVs are being built with showers, toilets, washing machines and even dishwashers. This means that they are also producing a lot more grey water than older RVs, whose grey water consisted mainly of the water used by hand washing the dishes.

While a free-camping area may have been able to cope with a bucket or two of grey water a day from each RV, the extra grey water produced by the newer RVs with all the mod-cons is much more likely to overload the capacity of the site to absorb it without creating any bad side-effects.

Problems which can occur include foul odours (indicating a build-up of bacteria) and increased numbers of flies and mosquitos, not to mention soggy ground or even mud. For these reasons, more and more land managers are insisting that RVs that use their free-camping facilities be ‘self-contained’ so that no grey water is left on site.

While grey water holding tanks are common in motorhomes (and have been for many years), they are not so common in caravans, mainly because water is heavy and, with the payload available to most caravans limited to around 300kg for a single-axle vans and 400kg for dual-axle vans, there’s little capacity to carry any significant amount of grey water. Then there’s the cost of one or more additional water tanks and additional plumbing.

WEIGHT CONSIDERATIONS

Before considering installing a grey water holding tank in your RV, make sure that you have sufficient payload available to carry the extra weight of the grey water, water tank and associated plumbing. To do this, load up the RV as you would for an extended trip (including full fuel, fresh water and gas tanks) and take it to a public weighbridge. The difference between the measured weight and the GVM or ATM on the compliance plate is the weight you have available. If this figure is not enough you have three choices; choose a smaller capacity grey water holding tank, increase the RV’s GVM or ATM, or forget about installing a grey water holding tank.

INSTALLING A GREY WATER TANK

In a RV, grey water is water that has been used like wastewater from the sink, dishwasher, shower or hand-basin, but excluding waste water from the toilet which is known as black water. Black water should never be mixed with grey water, nor should it ever be discharged on site except at approved dump points.

To store grey water in a holding tank, the tank must be lower than the waste outlets otherwise a pump will be needed to get the water into the tank. This presents a problem in RVs with showers because the shower waste outlet is normally at floor level (or only slightly above) and the tank is generally up as high as possible so that it does affect ground clearance, which means that there is little to no ‘fall’ to drive the water into the holding tank. This also means that when using the shower, the RV must be levelled such that the shower waste will be higher than the tank inlet so that water will flow into the tank and not over the floor.

Another thing to remember is that grey water produces foul odours when left sitting for any length of time. This means that, just like sewer pipes in your house, the grey water outlets need to be fitted with devices which prevent these odours generated from the water in the tank from coming back through the waste-water outlets into the RV. In your home these devices are usually ‘S’ or ‘P’ traps which block the odours by the water which remains trapped within the bend. However, in a RV which is subject to movement and vibration, the water in these traps might be dislodged due to vehicle movement and waterless one-way valves might be a better idea.

The other benefit that waterless one-way valves have is that they can prevent water coming back up the shower’s waste outlet while travelling. This can happen when a RV with a shower at the rear is climbing a hill because the shower outlet can become lower than the level of water in the grey water holding tank.

Another point to remember is that the grey water holding tank must be vented to allow air to escape when being filled and to allow air to enter when the tank is being drained. To work correctly, an open-ended vent pipe needs to be connected to the top of the holding tank with the other end located higher than any waste outlet to avoid overflow when the tank is full.

The outlet side of a water trap may also need to be vented, either with a vent pipe similar to the tank, or via an ‘air admittance valve’. These valves are designed to let air into the pipe when the air pressure inside the pipe is less than atmospheric pressure, thus preventing water being sucked out of the trap and removing the water seal. The valves close again automatically, to avoid the discharge of foul air, when the pressure in the pipe is equal to or greater than the external pressure.

Another important factor in is to use the largest possible diameter pipes so that the water does not fill the pipe as it flows towards the tank, which can cause air bubbles and poor water flow. Depending on the length of the pipe runs from the discharge points, additional anti-siphon or air admittance valves may need to be installed near these discharge points as well.

Finally, it’s a good idea to have a water gauge fitted to the tank so that know when it’s getting full – nobody wants the shower to back up and flood the floor of the RV!

BRIGHT IDEA

If it’s not feasible to locate a grey water holding tank in a position which is low enough for the grey water to flow into it via gravity, why not use a temporary vessel like a bucket or jerry can on its side to collect the water then either pour the water into a holding tank, grease trap or dump point (if available) or store in a re-sealable jerry can for later disposal.

NEED ADVICE?

Getting plumbing to work correctly can be a challenge to those who have not done it before. If in doubt, consult your local licensed plumber or ask your caravan repairer if they have a licensed plumber on staff who can give you some advice.

GREY WATER DISPOSAL

Disposal of RV grey water when free-camping remains a vexed issue. Before the introduction of grey water holding tanks, grey water was either collected in a bucket which was later emptied on nearby vegetation or a sullage hose was connected to the discharge point and the water allowed to flow onto the ground where the RV was parked. If staying for any period the hose was generally moved around from time to time to prevent water pooling or causing the dirt to turn to mud.

Obviously, for camping areas which are designated to be ‘self-contained’ (including rest stops), any grey water must be retained within the RV which then begs the question of how to legally dispose of the grey water once the storage is full.

One way is to empty the grey water at an approved dump point, just like the black water from the toilet. Another is to stop over at a caravan park or wait until you get back home and then drain the tank into the sewer via a grease trap.

There are also lots of disposal methods that you shouldn’t use; emptying the tank while travelling, emptying the tank into any stormwater or natural watercourse, emptying the tank on the ground at a rest area or layby on the side of the road, just to mention a few.