Prevents water backflow between washing machines and tumble dryers. If a washing machine and a condensation or heat pump tumble dryer are connected to a siphon connection, the waste water from one machine could be pumped into the other machine. A non-return valve in the waste water pipe prevents this backflow or back pressure. Suitable for drain hoses with an internal diameter of up to 10 mm. With 2 hose clamps 10 - 16 mm. Consumer advice: Simply cut the drain hose of the appliance at the desired point or fit a separate drain hose to the siphon. Insert the non-return valve and the hose clamps between the two hose ends and ensure that the embossed arrow points in the direction of the siphon. Tighten the hose clamps. Only suitable for waste water.