| 摘要 |
PROBLEM TO BE SOLVED: To enlarge internal space to facilitate inspection work and allow water flow, flowing into the interior, to flow out without staying inside, and perform construction work at a construction site easily in a short time regardless of the number and a connecting direction of connected straight pipes. SOLUTION: Upstream and downstream pipelines are respectively connected to the side part of a peripheral wall part 2. A nearly horizontal annular step part 5 is provided inside the peripheral wall part 2 to allow feet to be placed thereon during inspection. A hemispherical wall part 6 is provided at the inner periphery of the step part 5, and sewage from an upstream line 15 is collected into the hemispherical wall part 6 and then guided to a downstream line 8. An inclined wall block of almost sector shape provided with inclined faces of a specified angle in side cross section can be placed on the step part 5. When a center axis A of the upstream line 15 is in a higher position than the step part 5, the inclined wall block is disposed on the step part 5 along the center axis A to form a part of the upstream line 15 of the inclined wall block so as to be able to drill a hole.
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