If by any chance you do not know what type of system you have, the blowout method would be recommended in this case. When the water is drained, the boiler can be opened to drain the remaining water located between the backflow device and the cut off valve.You can get best solution with Professional Landscape Architects of this draining problem. When the water is drained, the boiler can be opened to drain the remaining water located between the backflow device and the irrigation valve. In other areas there can be a combination between manual draining and auto draining in the system on the pipe which is located between the sprinklers and the valves. If the sprinklers have check valves then you must pull up the sprinklers to ensure the water to drain out through the bottom of the body. If the back flow device works on ball valves, then you could open and then close the isolation valves on the device as China UPVC Butterfly Valve Suppliers many times as needed to ensure that any remaining water has been drained from it. In the same case which the sprinklers have check valves, then you should pull them up to allow proper water drainage through the bottom of the body. Pennella's Landscape Designs, LLC To minimize the risk of freezing damage which is caused by the remaining water after irrigation draining, the system must be made winter proof so that methods such as manual drain, blowout and auto drain systems must be installed. Activating the system means that it must be shut off and then activated to relieve the systemâ''s pressure. Once the water is drained, the drain valves can be closed manually. Automatic drain method With the valves located at the end and low points of the piping, they will automatically open and relieve the water if the pressure is below 10 PSI. Outdoor Living Areas Manual drain method With the valves being located at the same points as above, you must simply shut off the irrigation system's water supply and then manually open the drain valves. Click here to get more information to prevent your house from draining!. More steps Once the water is drained from the irrigation system, make sure to disconnect the air compressor to release the remaining air pressure.