Abstract: Descaling elements for cleaning cooling water tubes within a steam condenser are received within a water soaking vessel. A wire net is stretched within said vessel, and said vessel is charged with water until the water level reaches a predetermined limit line above said wire net. The presence of the wire net prevents the descaling elements from being floated up to the water surface. A considerably large space is formed between the water surface and the ceiling of the vessel. Said space communicates with an evacuating device for deaerating the interior of the vessel, and no air filter or air separator is required for said evacuating device.