A system for flushing a vacuum toilet in an aircraft, with a bowl drain for removing toilet waste water from a bowl, a drain line, a bypass flow line for feeding-in air, a drainage valve and a waste water line. The bowl drain and the bypass flow line are connectable to the drain line, and the drainage valve on the input side is connectable to the drain line, and on the output side is connectable to a waste water line. In an implementation of the vacuum toilet as a vacuum urinal, the system may provide either water flushing or waterless flushing.