| 摘要 |
PROBLEM TO BE SOLVED: To provide a catch basin allowing a plug of a cover of an inspection cylinder to be removed to open an opening, coping with the vacuum state or pressurized state of the catch basin and allowing the opening of the cover of the inspection cylinder to be closed with the plug when the state changes, with hardly any danger of losing the plug. SOLUTION: A plug 6a is provided with a bulge part 61a at the upper part, and a resilient bulge part 62a at the lower part. An opening 5a is provided with a diameter-enlarged stepped part 52a (a locking part) at the lower part of a cylindrical part. When the plug 6a is fitted into the opening 5a, the lower bulge part 62a is locked to the diameter-enlarged stepped part 52a at the lower part of the cylindrical part, so that there is hardly any danger of the plug 6a falling from the opening 5a.
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