A waste water drain apparatus (1) is to be attached to the fuselage belly (2) of an aircraft. The apparatus (1) essentially includes a drain pipe (3), an aerodynamically shaped fairing (7) enclosing the drain pipe (3), an attachment flange (6) for connecting the apparatus to the aircraft, at least one temperature sensor (9), and either at least one heating element (8) or hot air inlet (13) for heating the drain pipe (3). An inlet end (4) of the drain pipe (3) is to be connected to a waste water system of the aircraft. An outlet end (5) of the drain pipe (3) exits rearward at the trailing edge of the fairing so that the lengthwise axis of the drain pipe outlet is substantially parallel with the air flow during flight. Either hot air is caused to flow along the drain pipe (3), or heating elements are arranged near or on the inner surface of the fairing (7) at least at the area where the drain pipe outlet end (5) passes through the fairing (7) and near or on the inner surface of the attachment flange (6) at the area where the drain pipe (3) passes through the flange (6). Freezing of the drain pipe is prevented and waste water can be drained at any time during flight.