Self-drainage three-way threading box

The utility model discloses a self-drainage three-way threading box, which solves the problems that the existing three-way threading box discharges accumulated liquid and possibly causes foreign matters to enter a threading guide pipe. According to the technical scheme, the automatic drainage device comprises a three-way box body, a water outlet in the lower end of the three-way box body is connected with an automatic drainage device, the automatic drainage device comprises a shell with a drainage hole in the bottom, a trapezoidal weir is arranged on the upper section in the shell, an elastic assembly is arranged in the center of the bottom, and a valve plate is arranged at the upper end of the elastic assembly. And the valve plate is in contact sealing with an outlet at the lower end of the trapezoidal weir. The box is simple in structure, easy to operate and good in universality, accumulated liquid in the box body can be discharged in time, and rainwater can be prevented from flowing backwards or insects ca