Abstract: An improved control system (apparatus and method) for a low-water/air-flush toilet system which effects a simultaneous reduction in the amounts of water and compressed air required for flushing the toilet. The system employs an improved spool valve control mechanism to initially water-flush the bowl portion of a toilet combination and thereafter to air-flush a base portion of the toilet combination, in a sequentially controlled operation. The improved control system is particularly adapted to compact biological or chemical waste treating systems for mobil units (e.g., in rail cars, buses, boats, aircraft, etc.), but is also effective with conventional toilets or waste treating systems.