PURPOSE: To connect or disconnect a casing accurately against a storage tank by providing a sliding pipe supported by a spring having a suction port which comes to fit with the suction port of the casing when the pump body is lowered.
CONSTITUTION: When pump body 3 is lowered inside casing 2, flange 3b strikes the upper end surface of sliding pipe 10, which compresses spring 12 and lowers pump body 3. When sliding pipe 10 descends until its lower end surface strikes step 9a, suction port 10a comes to fit with suction port 2a of casing 2, and the storage tank and the inside of casing 2 are connected each other. When pump body 3 is raised, sliding pipe 10 is pushed up by the restoring force of spring 12, and it is stopped when its upper end surface strikes projection 2b. Subsequently, pump body 3 is further raised, and suction port 2a and suction port 10a deviate from each other, so that the connection between storage tank and the inside of casing 2 is interrupted. Casing 2 and sliding pipe 10 are sealed by packing 11.