The Stop Silent Light backwater valve applies pressure to the diaphragm by accumulating waste water inside the valve. The sealing lip is opened upwards and releases the waste water flow. If the waste water flow is at a standstill, the backflow valve closes again by lowering the sealing lip downwards. If a backwater then occurs, the rubber membrane is filled and pressed against the pipe wall. This has the advantage that the backflow valve closes airtight.