Stub for discharging drained fluids for a propulsion unit. The stub includes a cavity for storing the drained fluids and at least one orifice for discharging the fluids contained in the storage cavity, and elements for measuring a difference in pressure outside the stub and a member for draining the storage cavity. The member is able to move between a first position of closing the discharge orifice and a second position of releasing the orifice, and is configured so as to move from the first to the second position when the difference in pressure is greater than, or equal to, a predetermined value.