System for filling a tank comprising a pipe head and a fill pipe extending between the pipe head and the tank. The pipe head comprises a chamber with an inlet opening that connects to the atmosphere and an outlet opening that connects to the fill pipe and a stopper being movable between open and closed positions to open or close the access to the fill pipe, the head inlet and outlet openings being sized and arranged to allow introduction of a filling nozzle into the fill pipe through the pipe head when the stopper is in its open position. The fill pipe comprises or is preceded by a local restriction designed so that the cross section of the passage for the nozzle is substantially reduced to the outer diameter of the nozzle. A degassing connection links the fill pipe and the pipe head outside of its outlet opening.