How do you flush the radiator on a '99 Chevy Silverado?

Drain the radiator by removing the plug on the bottom of the radiator or by removing the lower rad hose. Take the thermostat out which is at the engine end of the upper hose. Start the engine and run water from the garden hose through the radiator letting it flow out the upper rad hose until it is clean. If it has buildup in the radiator you will want ot run some commercial radiator cleaner through it. When it is clean, drain all of the water out and install 2 gallons of coolant and the thermostat.. Dispose of used coolant properly.