With our tube flap, even a slight accumulation of waste water is sufficient to exert a small pressure on the membrane. The membrane presses a sealing lip upwards and the waste water can flow. If the wastewater flow is at a standstill, the sealing lip closes and the pipe flap closes. In the subsequent backwater, the rubber membrane is filled and lies against the pipe wall. This prevents gas movement and also serves as an odour damper.