PURPOSE: To forcibly drain water, flowing through the drain port of a sink to a casing with bottom, through utilization of the water pressure of city water and to perform forced drainage only when water is discharged through a city water faucet.

CONSTITUTION: A casing 3 with a bottom, a drain input chamber 27, and an impeller chamber 28 are provided. A turbine impeller 42 is arranged to an impeller chamber 28, and an impeller 43 for drainage is arranged to the drain input chamber 27. When a city water faucet 39 is opened, city water flowing through a city water line 37 to the impeller chamber 28 is fed from the impeller chamber 28 to the city water faucet 39 for outflow. A turbine impeller 42 is rotated by means of the water flow of city water flowing to the impeller chamber 28, the impeller 43 for drainage rotated following rotation of the turbine impeller forcibly drains water flowing to the drain input chamber 27.