The device has a sealing unit (14) occupying a liquid releasing position and a liquid blocking position, and immobilization units (60) for immobilizing the sealing unit in the blocking position and preventing the sealing unit from occupying the liquid releasing position. The immobilization units exert support on the sealing unit and are activated when a detachable cap (11) is mounted on the device, where the immobilization units are carried by the cap. An exterior cover covers the sealing unit, and the immobilization units are formed by a projection in the form of an annular groove (60).