A gas ejection cone includes a cylindrical-shaped front cone portion, a conical-shaped rear cone portion, a ventilation tube and a support bearing of this drainage and/or ventilation tube. The ventilation tube extends inside the cylindrical-shaped front and conical-shaped rear cone portions and emerges at the end of the conical-shaped rear cone portion. In particular, the conical-shaped rear cone portion includes a front sub-portion connected to the cylindrical-shaped front cone portion, and a rear sub-portion removably secured to the front sub-portion. The rear sub-portion is further equipped with an outlet port of the ventilation tube.