The Rear Evacuation Valve (RSV) is a gate valve installed in the rear of the toilet's waste tank and gives you direct access to the waste tank and its contents. The RSV is installed in portable toilets that are situated in a location that has access to a sewer connection point or septic system. The RSV enables a gravity empty of your toilet by positioning the toilet above the location you are going to empty the tank into and opening the valve, after connecting a hose (it is quite messy if you don't use a hose). The RSV is also an ideal addition to a trailer mounted toilet that can be positioned next to a sewage access point e.g. recreational vehicle points provided by councils on major roadways used by caravans. Things to consider: You generally will need to move the toilet from its normal location to the sewage access point. Do you have equipment to move the toilet eg tractor, forklift etc. A full portable toilet can weigh up to 500 kg. You will need a hose connected to control / guide your waste to the desired location. All waste disposal is conditional on your local council regulations. You can add an RSV to an existing toilet by buying the valve from Merlin. We also sell the hose kits. It costs approx extra to add the valve to a toilet, however, it will save you the ongoing cost to have the toilet pumped out by a service contractor. Service contractors will not use the valve to pump out a toilet — they will access the waste tank via the bowl assembly.