any other adequate material the base of external bell 3 and cap 8 are arranged in a complementary manner or provided with complementary junction means enabling them to be assembled rigidly in a removable manner and at the same time enabling passage of water between the base and the cap cap 8 is for example provided with three guiding and latching forks 11 spaced at 120 degrees and between the branches of which base 3b of external bell 3 is engaged and retained the internal branches 11a of such latching forks 11 being provided with vertical ribs 11b acting as guides to float 6 during vertical movements of such float float 6 is a submersible float it is equipped with a blocking device 12 which is axially and vertically mobile this blocking device being housed concentrically in float 6 from which it emerges by its lower portion equipped with a capsular flange 12a this latter element constitutes a valve that can be pressed against its seat 4a constituted by the edge of lower orifice a of the overflow tube thus ensuring the buoyancy of the float or be distanced from the seat so as to enable entry of water into the float driving the submersion of such float and consequently the fall of valve 5 on its seat 7 of central orifice e blocking device 12 advantageously comprises a tubular body preferably cylindrical having a tip provided with a punched upper wall for example constituted by a transverse bar 12b at the center of which a hole 13 is arranged for passage of a transmission rod 14 on the other hand the tubular body of the blocking device is provided externally and laterally with one or several abutment wings.