A filler device for a fluid tank, including: a filler duct; a first stopper, for preventing overfilling of the tank, and a second stopper for preventing fluid from leaving the tank in unwanted manner; a first float mechanically connected to the first stopper such that, on being placed in a predetermined position, the first float closes the first stopper; and a holder system for holding the second stopper, which system, when fluid leaves the tank, closes the second stopper, and when fluid enters into the tank, opens the second stopper. In an operating position of the device, and under effect of a heavy element, the holder system acts continuously on the second stopper, tending to maintain the second stopper permanently in its closed position.