A drainage mast able to drain effectively the liquid contained in the compartment of an aircraft when the pressure within the compartment is lower than the outside pressure without using any pressure control active device and without causing any significant perturbation to the aerodynamic behavior of the aircraft. The drainage mast is configured with a cross section area decreasing from its entry section to the compartment to its outlet section and is disposed at an acute angle α relative to the compartment in the airflow direction. The entry and outlet sections have two perpendicular symmetry axes of different length, the entry section is arranged with its longer axis of symmetry substantially parallel to the airflow direction. The drainage mast has a symmetrical configuration with respect to a plane substantially perpendicular to the fuselage envelope passing through the longer axis of symmetry of the entry section.