A low pressure is exerted on the Stop Silent Light membrane in case of a low accumulation of waste water. The sealing lip is then opened upwards and the fluid can flow out. When the sewage disposal stops, the sealing lip is restored and the non-return valve closes. During the water return, the rubber membrane is filled and pressed against the pipe wall. This makes it impossible for the gas to move and ensures that bad pipe odours do not escape into the cellar.