Secondary sedimentation tank siphon dredging device

The utility model relates to the field of siphon dredging, and provides a secondary sedimentation tank siphon dredging device which comprises a submersible pump, a washing main pipe, a washing branch pipe and a washing ball valve, the submersible pump is installed in a clear water area in a secondary sedimentation tank, the washing main pipe is communicated with the submersible pump, the washing branch pipe is communicated with the washing main pipe, and the washing ball valve is connected with the washing main pipe. The flushing branch pipe extends into the siphon pipeline, the flushing ball valve is mounted on the flushing branch pipe, and the flushing ball valve is positioned above the water surface of the secondary sedimentation tank; the expansion pipe is arranged at the bottom of the siphon, the expansion pipe opening mechanism is arranged to open the expansion pipe, when sludge is accumulated at the bottom, the sludge can be effectively discharged, meanwhile, the flushing mechanism is arranged, the slu