To prevent water from leaking by placing, on the inner surface of the above-water end of a rectangular tube curved at almost right angles,a cylindrical connecting tube that fits around a drain pipe, and providing a plurality of elastically-projecting pressing pieces through the notching of the inner peripheral surface of the connecting tube.

This drain elbow A having a rectangular cross section is curved into an approximately L shape. A cylindrical connecting tube 2 that fits around a drain pipe is placed on the inner surface of the above-water end of the elbow A. The connecting tube 2 consists of a step, which forms a space 24, and a pipe 21. A plurality of pressing pieces 22 that elastically project inward are provided at equal intervals along the circumferential direction on the inner peripheral surface of the pipe 21, and the pipe 21 is fitted around the drain pipe C constructed in a wall surface D. Thus, a uniform space is formed around the drain pipe, enabling stable sealing work execution by using silicon sealant, etc.