PROBLEM TO BE SOLVED: To provide a method for easily attaching a drain pipe to an existing drain pipe at low cost, a fixture used for the method, and a boring tool used for the method.SOLUTION: A fitting method is used for attaching a drain pipe 42 between a cleaning unit 40 for a water closet and an existing drain pipe 27 when the cleaning unit 40 for the electronic control type water is attached to a cleaning unit 25 for an existing water closet. In this method: a fixture 50 having a cylindrical part 52 to which one end 46 of the drain pipe 42 can be attached and which communicates with the drain pipe and a stationary portion 54 for being fixed at a prescribed position in the existing drain pipe 27 is used; the fixture 50 is attached to the prescribed position in the existing drain pipe 27; a boring tool 75 is inserted from the cylindrical part 52 of the fixture 50 to bore a hole in the drain pipe 27; the boring tool 75 is removed from the fixture 50; the other end 45 of the drain pipe 42 is connected to th
