A non-return valve is placed on the hose of your enema to stop fluid from flowing in the opposite direction up the hose and back to the enema machine. This device is particularly useful in that sometimes mucus and faecal particles are sucked back into the hose during the enema procedure and these particles fall back into the enema cistern itself. This contaminates the system and makes it less hygienic, as it must be washed every time after use when this occurs. The non-return valve does not allow anything to penetrate back to the enema and, accordingly, nothing could contaminate the enema cistern, leaving only clean water. Extremely useful device. We advise you to order it. Comes with all the necessary connectors to easily attach to your hose. Its black half should point to the tip.