Kinda depend on how it was winterized, but you just run water through everything (I start with the closest spigot to the water inlet). Check the water heater to make sure the drain (or Anode) is closed, close the Water heater bypass valve and let the air out by turning the hot water on somewhere and then just run water everywhere till no mor air bleeds out. You also may want to put some water in the water tank and pump that out a couple times.
And then sanitize the whole system with chlorine at 100 ppm. 1/4 cup bleach per 15 gallons of fresh water. Pump it through all of the water lines. Let it set for a few hours or over night and then flush out with fresh water.
2007 Chevy 2500HD Classic LBZ Duramax/Allison (Stock)
2005 Bigfoot 1500C8.2 AWESOME