PURPOSE: To prevent leakage from a connecting section to drain, etc., in an upper section even at the time of a large amount of rainwater by forming recessed bent sections to pipe walls on both sides of a lateral pipe section in the lower section of a vertical pipe section and forming projecting sections projected to a lower section to the internal surfaces of the insides of the bent sections.

CONSTITUTION: Projecting sections 14 are projected and formed downward from the internal surfaces of the insides of recessed bent sections 13 shaped to pipe walls on both sides of a lateral pipe section 12, and the leakage of rainwater falling from drain in an upper section is inhibited. Even when falling rainwater falls on the bottom wall of the lateral pipe section 12 and rises along both side walls and collides with the internal surfaces of the recessed bent sections 13 at that time, the formation of small eddies and upward splash are suppressed owing to the projecting sections 14.