Blowing out a sprinkler system is crucial to prevent freeze damage. Typically, you'll need an air compressor to push out water from the system. Start by attaching the compressor to the blow-out port, and run it until no water remains in the pipes. It's important to use the right pressure to avoid damage. Is this something you're planning to do yourself, or are you considering hiring someone? Have you winterized your sprinkler system before?