PURPOSE: To improve efficiency by a method wherein by using a number of vertical type pipes, heat exchange is effected, two on-off valve parts are mounted to a pipe body, with the aid of a pump, a circulation feed to a tank and forced discharge from the tank are performed, and only through operation of the two on-off valve parts, the feed and discharge of liquid are executed.

CONSTITUTION: A raw material solution in a raw material tank 30 is fed, in a heated state, to a given place, in order, through a suction port 3, an on-off valve part 5, a pump 11, an on-off valve part 4, a feed port 6, a feed part 8, a pipe 23, a discharge part 9, a pipe 10, and a delivery port 2. With the on-off valve parts 4 and 5 controlled, a raw material solution in a tank 7 is forcibly fed to the outside from the feed part 8, in order, through the on-off valve part 5, the pump 11, and the delivery port 2, and this process is used for cleaning of the interior of the tank 7. In this case, hot water heated by a boiler 12 is fed in a case 20 in the tank 7 to heat the pipe 23. When the on-off valve parts 4 and 5 are controlled as shown in A and B, circulation within the tank 7 and circulation to the raw material tank 30 can be effected. This constitution executes a flow by means of vertical type pipes without the occurrence of choking, prevents the occurrence of a error in operation, and enables the high- efficient feed of a raw material solution.