Running water and a flushing toilet are essentials that many people cannot be without when using a camper. The vehicle must have a sufficiently large reserve tank of water (or provide for hookups to a water source) and a fully functional system of delivery. The system must comprise a water tank, a pump that works when the camper is parked remote from a power connection, appropriate appliances, plumbing that feeds each appliance and a sewage system that accepts, stores and allows for the disposal of waste. Putting a plumbing system in a camper is a complex but rewarding project.
Decide on a water tank that will suit your purposes. The size will be a trade-off between the amount of water it will store and the amount of space it will take up. The tank must be low in the vehicle -- as close to the chassis' centre of gravity as possible -- and in a place where hoses can be run to and from it without great inconvenience.
Decide on a pump that works when the camper is parked remote from a power connection. The pump must run on 12-volt electricity and be of the "demand" type, which means it must automatically switch on when it senses the pressure in the system is lowered, such as when a tap is turned on, and then turn itself off again when the pressure returns to its set value. Locate the pump close to the water tank, and fit it with a one-way valve to stop water from entering the storage tank and causing it to overflow.
Decide on the appliances necessary for you to fully enjoy your camper. A typical system comprises sinks in both the galley and the bathroom, a toilet and a bath/shower. Many campers also include a propane-fuelled water heater.
Draft a plumbing installation plan that feeds fresh hot or cold water to each appliance. Consult the manufacturer's literature delivered with the water tank and all the appliances, and buy pipe that will transmit an adequate volume of water to each. Typically the appliance fittings will be 5/8-inch. If so, buy 5/8-inch hose rated for potable water. You will also need enough hose clamps to complete your project.
Draft a sewer installation plan that accepts, stores and routes waste water. All the appliances must drain into a system of pipes installed the same as any household system, but the holding tanks beneath the vehicle are unique to a camper's requirements. You'll need a grey-water tank to hold waste from the sinks and showers, and a blackwater tank to hold waste from the toilet. Place the blackwater tank immediately below the location of the toilet, so the toilet outflow can be attached directly to the tank inlet. Both tanks must also have a method of transferring held waste to a dumping facility.
Plan two water inlets. One will accept water from an unattached hose and funnel it downward into the unpressurized storage tank, from which water is pressurised by the on-board pump. The other inlet must be of the type to which you can attach a pressurised hose so that the camper's plumbing system is pressurised by the main. Called a "city water" inlet, it must have a pressure regulator so the main's pressure is not introduced into the camper's plumbing.
Place the city water inlet in the rear driver's side quadrant. Situate it with the other hookups so hooking up at campsites is convenient. Don't fit it directly over the cargo bay where the shore power cord is kept. You must have a potable-rated water hose to connect this fitting to the city water supply.