The invention relates to a filler spout comprising a tubular body having mounted therein both a valve member extending facing an inlet orifice of a distribution chamber and also a shutter arranged downstream from the valve member and rigidly connected thereto in such a manner as to extend facing an outlet orifice of the distribution chamber. An actuator is coupled to the valve member in order to move it between an extreme opening position and an extreme closing position, the valve member possessing an intermediate closing position in order to form a suction piston when the valve member is moved from the extreme closing position to the intermediate closing position or from the intermediate closing position to the extreme closing position. The shutter includes a channel opening into the distribution chamber and facing the outlet orifice of said distribution chamber so that the channel is always unobstructed regardless of the position of the valve member.