A water flushing system for a pressurized subterranean water distribution system includes an inlet conduit for receiving pressurized water from the subterranean water distribution system; an outlet fluidly connected to the inlet conduit for discharging pressurized water in the inlet conduit downwardly towards a drain; and a control valve for controlling the flow of pressurized water in the inlet conduit. The water flushing system further includes one or more of the following features: a freeze protection assembly, a detachable coupling system, a dechlorination system, and a backflow prevention system.