The double hose nozzle is only suitable for connecting (prewall) to siphons, as the connection nut is flat sealing. The double hose nozzle is used to drain waste water via siphon. The blue sealing disc is used to close a connection when not in use. No additional seal is required when using the duckbill (backflow preventer). The collar of the duckbill (backflow preventer) seals. Only suitable for use on washbasins and sink siphons. Nuts must only be tightened by hand, please do not use tools such as pipe wrenches, etc., otherwise they may break. The assembly should be checked after 24 hours and, if necessary, as the seal swells over time and the full sealing effect is slightly delayed. Not suitable for use on the flush-mounted siphon. Please use item 4063 for this