An improved human waste collection system was developed in 1985 using a piston and cylinder which collects, compacts, and stores in replaceable volumes human waste including cleaning material. Disposable pads on the piston face seal and clean the cylinder and occlusive air valves. Airflow provides waste entrainment and temporary retention. A series of prototypes including an automatic one-button operation unit was built and ground tested. A manually operated prototype with a number of test features including variable airflow was flown and evaluated on Shuttle flight STS-35. Performance was nominal. An airflow of 45 CFM (1.27 m3 min-1) was found to be adequate. Mean stowage volume of waste and hygienic material per use was 18.7 in3 (306cm3). It now appears that such a unit can provide adequate collection of human waste and all associated hygienic material with minimum overhead of machine size, complexity, and power, and minimum logistical support including maintenance, cleaning, operating materials, and storage space for Shuttle or Space Station.