| 摘要 |
PROBLEM TO BE SOLVED: To prevent spiral plates of a lower guide passage from being damaged by solid materials such as stones included in sewage. SOLUTION: The intermediate guide passage 3 of a sewage stack comprises a pipe body 31 and the spiral plates 32 provided on the inner periphery of the pipe body 31. One or a plurality of spiral plates 32 having at least one pitch are provided at set intervals. The solid materials collide with the spiral plates 32 to be damped before freely dropping over the length of the intermediate guide passage 3, i.e., before reaching a large dropping speed, and drop along the spiral plates 32.
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