Abstract: An aircraft toilet system includes a holding tank and a discharge pipe which extends to a service panel located near the skin of the aircraft. A poppet valve is located near the outlet end of the discharge pipe. Leakage of fluids past the poppet valve is corrected in a first embodiment by pressurized cabin air which is ported to a downstream side of the poppet valve and by venting the upstream side of the valve to the atmosphere. In a second embodiment, high pressure air from the aircraft's environment control system is ported to the downstream side of the valve. The resulting pressure differential holds the valve against its seat, and prevents fluid leakage in the event of a damaged valve seal.