assure the reliability of the method and of its operation measuring sensors for temperature 10 and the level 12 of the confining liquid can be installed the entire apparatus is surrounded by external housing 14 the self disinfecting drain trap can be provided with instruments of different complexities in accordance with the requirements resulting essentially from the type and the germ content of the waste water and the operating type of the drain trap according to the invention the self disinfecting drain trap is always provided with at least one ultrasonic or low frequency irradiation device at least one heating or thermostating device and with the associated control technology the self disinfecting drain trap in fig1 in the form of a customary bottle cylindrical siphon is designed with maximal instrumentation and ultrasonic device the self disinfecting drain trap designed in this manner assures maximum reliability for all such drains used in an irregular manner and with which there is a danger of drying out in the intervals between use the level control 12 is the main signal transmitter that means that both the heating 6 and also the ultrasound 3 can only be operated given a sufficient level the heating capacity.