| 摘要 |
PROBLEM TO BE SOLVED: To provide a case structure of a septic tank capable of preventing a crack which results in a leakage of water to be treated from occurring in advance even if a shock is applied and reducing the cost for laying underground. SOLUTION: In the case structure of the septic tank in which a water treating space for biologically treating raw water of the water to be treated by accepting thereof is formed inside, the case X is made of resin material, a plurality of projected ribs R projecting from the surface of the case X are installed on the outer surface, and the part where a projected ribs R are set is thicker in wall thickness than the part where the projected ribs R are not set in the case X.
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