PURPOSE: To prevent a filter from choking by providing nozzles on the hold side of a drain port filter in the bottom layer of a hold to jet water in the biginning of slurry loading and preventing drainage from the bottom layer during the loading.

CONSTITUTION: A drain body 24 with a filter is provided at the bottom of a hull 2, while an overflow port 18 is provided in the upper part. In the bottom drain port 24, a filter 25 is furnished in front of a drain padage 23, while nozzles 26 are fixed on the side of front hull for jetting high-pressure water in the biginning of slurry loading. During the slurry loading, the drain port 24 is prevented from draining. This construction permits to prevent the filter from choking due to powdered rocks in coal slurry. At the drainage after the loading, filter is difficult to be chocked due to rough coal grains concentrated near the filter, and water can be reduced in the slurry.