Shut off the water valve to the sprinkler system, turning the cutoff knob clockwise.
Unscrew the coupler that connects the main sprinkler line to the water pipe near the cutoff line.
Lower the line to the ground so it is level with the main sprinkler line to drain the water. Your system may be equipped with drain valves that open automatically when the water pressure falls below a certain level. If you do not have an automatic system, continue the draining steps.
Screw on the adapter to the hose on the air compressor. The adapter twists half a turn clockwise to lock onto the hose.
Fasten the other end of the adapter to the main line of the sprinkler system, turning the adapter to the right to tighten it.
Turn on the air compressor and run it until the sprinkler system is completely drained of water. When the sprinkler jets in the lawn stop spraying water, you're done.