PURPOSE: To automatically discharge water inside a soil and sand housing chamber by a method in which a weight and a boot having the soil and sand housing chamber inside are housed in a bucket frame, a bucket is provided at the lower part, and a drainage canal with a check valve is provided in the weight.

CONSTITUTION: By extending an oil-pressure cylinder 11 in a shrunk state, bucket halves 8 in opened state are closed to scoop up soil and sand into a soil and sand housing chamber 7. In this case, a weight 12 is pushed up by a fluid pressure, a boot 15 is extended, a drainage canal 17 is closed by a check valve 18, and back flow of water from a drainage chamber 16 to the housing chamber 7 is interrupted. When the weight 12 goes down by its own weight, the boot 15 is folded, the housing chamber 7 is shrunk, water omnipresent in the upper part flows out to the drainage chamber 16 through a labyrinth 19, the drainage canal 17, and the check valve 18, and soil and sand alone remain in the housing chamber 7.