I have a 2006 Express, so this is not specific to your model, but I believe the answer is probably the same. The water heater has a drain on the bottom, below the inlet and outlet (looks like a hose faucet). By opening that, it should drain. I don't believe there is a drain for the water tank and if there was, I wouldn't know how to get to it. I drain the system by running the water til it runs out. To get the system up and running in the spring is the hardest part since there is always some residual non-toxic antifreeze left. I constantly put in some water and run til "empty" trying to get as much out as possible. Then fill tank with some bleach and run thought all hoses to clean entire system, then run til empty a couple times to try and get all of that out. Even with all of that, I still don't drink the water.