The device that I purchased, has 3 valves on it. One valve that controls the garden hose water flow. One valve that controls the flow of water towards the heat exchanger through the impeller, and one valve that controls the flow of water from the leg.
To flush the cooling system -- I'd hook up the garden hose connected to a SaltAway dispenser and turn it on on the Fresh Water setting, start the engine, open all 3 valves. I'd then close off the valve for the leg and switch the SaltAway so that the concentrate was flowing through the cooling system. Once I saw the soapy bubbles come out of the leg, I'd shut off the engine. Could back-flush the leg at that point as well by opening that valve. I'd then close off the garden hose valve.
To winterize, you follow the same steps, but you put a length of garden hose in a bucket of Anti-Freeze (the safe to Animals kind) and run it liberally through your cooling system. Note that I never did this so can't comment on how safe that is in terms of getting all the water out to prevent freezing.