Here is how I winterized mine. There is a drain outside the slide near the fridge; I opened that up when I did the other low points. Take the water filter out of the fridge. Then just leave your water pump on for a few hours with the plumbing antifreeze hooked up until you get pinkish ice cube. Took mine two cycles of cubes.
It's my understanding that if you don't remove the water filter it will take a lot longer.
Here is a pic of how my cubes came out. Hehe.