PURPOSE: To permit to improve safety by a method wherein the liquid of a supplying source is sent from a suction port to a delivery port through a liquid reserving tank and adherence of solid material to the inside of a pump is prevented.

CONSTITUTION: The opening and closing valve 11a of the suction port 2 is opened, the same valve 11b of the delivery port 3 is closed, the opening end of a suction air introducing pipe, connected to the suction port 2, is faced to an arbitrary source of supplying liquid and a vacuum pump 4 is driven. When the pressure in the liquid reserving tank 1 becomes vacuum by the driving of the vacuum pump 4, the liquid in the supplying source is induced into the liquid reserving tank 1 through the suction port 2, therefore, the liquid in the supplying source will never pass through the pump and the solid materials will never be adhered to the inside of the pump.