1. Locate what looks like a square peg on a drain cap assembly on the Brass Check Valve, if there is one. Usually, there will be either test cocks or a capped drain assembly. For this method, you need a wrench the size of the square nut on the cap to remove it and large-diameter flexible landscape tubing to route the water to your drain source.
2. Turn off the main valve to the irrigation system. This prevents new water from flooding the system as you drain the old. Make sure the valve in the double check assembly is closed