than the inner diameter of the passage formed in tubular body 3 and both lance 2 and the inner diameter of the passage formed in tubular body 3 can be of circular cross section lance 2 is fixed in body 3 in line with a protruding coupling piece 34 in the vicinity of the opening 112 the longitudinal axis 21 of lance 2 is parallel to the longitudinal axis 33 of the part of the evacuation passage that is located at end 32 of body 3 however axis 21 is offset above axis 33 to leave a space in the evacuation passage in body 3 below lance 2 for the flow of large particles out of tank 110 piece 34 is provided to connect lance 2 to a faucet 400 of the type that is available in all homes via a flexible tube 5 and a flexible attachment piece 61 preferably made of elastomer and having an elastic inlet opening 61 that can be fitted to virtually any type of faucet simply by pushing a connecting piece 6 which may have a bulbous form over the outlet end of faucet 400 connecting piece 6 is connected to flexible tube 5 by a connecting element 51 which may have a tapered form thus connecting piece 6 can easily be replaced with any other type of connecting.