PURPOSE: To use a single drain socket at different drain pipe positions by forming a trap housing section like a bent pipe, and further forming a recess on the internal surface of the lower section of the upper end opening of the trap housing section for receiving drain flowing down through a trap and introducing the drain toward the internal space of the trap housing section.

CONSTITUTION: A trap housing section 3 is formed like a bent pipe and the upper end opening 3a thereof is kept eccentric from a drain pipe coupling section 4. Also, a recessed drain receiving surface 3b and a drain guide surface 3c are formed on the internal surface of the lower section of the opening 3a. As a result, drain flowing down from a toilet B via a trap C is received with the surface 3b and, then, caused to flow down toward the internal space of the section 3 via the surface 3c. In this case, a water flow is actively generated in the section 3 and, then, guided to a horizontal dam 4a. Thus, a pipe passage from a toilet B1 to the lower side of the section 3 via the trap C acts as a syphon tube, thereby facilitating the discharge of drain. According to this construction, the generation of a syphon phenomenon is ensured.