Abstract: A scouring system for automatically scouring an empty liquid reservoir, for example, a flood basin, includes at least one scouring liquid chamber with a scouring opening in communication with a siphon-like scouring duct. Any liquid contained in the scouring liquid chamber is retained in the scouring liquid chamber by means of atmospheric pressure when the liquid level drops in the reservoir. An air inlet opening which can be closed by a ventilating valve is provided in the ceiling of the scouring liquid chamber. The ventilating valve includes a pressure box with a diaphragm which is deformed when compressed air is applied and closes the air inlet opening. A vacuum blower is connected to the scouring liquid chamber through an intake line and to the ventilating valve through a pressure line. The vacuum blower initially closes the ventilating valve, the scouring liquid chamber is evacuated and filled with scouring liquid.