Plumbing apparatus (10) for incorporation in a waste pipe system comprises a tubular body having an inlet (14) for connection to an upstream waste pipe and an outlet (16) for connection to a downstream waste pipe. A one-way water valve (22) is provided in the body and is arranged to permit flow from the inlet to the outlet and to prevent flow from the outlet to the inlet. An air valve (24) is mounted on an upper portion of the body and is arranged to permit flow of air into the body and to restrict flow of air out of the body. In the event of negative pressure in the downstream waste pipe system the air valve opens to allow air to be drawn into the system. In the event of positive pressure in the downstream waste pipe system the one-way water valve closes.