An aircraft drain/fill fitting includes a housing adapted for being fitted into an opening between an aircraft interior and an aircraft exterior. The housing has an interior housing segment fluidly coaxially communicating with an exterior housing segment to define a liquid flow path therethrough, and a heater for applying heat to the interior housing segment. A hollow insert element is positioned in the interior housing segment in heat transfer contact with an inner wall of the interior housing segment. An elongate heat transfer probe is positioned in heat transfer contact with the hollow insert element and extends into the exterior housing segment to reduce the incidence of freezing of liquid in the exterior housing segment.