How do you flush the cooling system 1999 chevy venture?

On the bottom corner of the radiator on the passenger side, there'll be a drain plug. Turn it counterclockwise until it comes out - and be sure to set some drip pans under it prior to doing this. This will drain the coolant. Once it stops draining, take a garden hose and insert it into the radiator cap opening. Turn the water on, and crank the motor. Let the motor long enough for the thermostat to release water through the cooling system. When you get clear water after the thermostat engages, you can cut the engine off and shut off the hose.