Drain masts of commercial aircraft need to be heated in order to prevent freezing caused by the low outside temperatures when the aircraft travels at a corresponding altitude. An exemplary embodiment described in the application pertains to a drain system for an aircraft that can be used for draining liquids or gases from the aircraft or for drawing air into the aircraft. In this case, the liquids or gases are heated by means of a coolant that receives its thermal energy from a thermal or electrochemical process being carried out on board the aircraft. Consequently, the waste heat produced by the thermal or electrochemical process being carried out on board the aircraft, for example, a fuel cell process, can be carried off outboard via the drain system. In addition, the coolant can be advantageously utilized for cooling the thermal or electrochemical process.