[Xeen]

To flush the cooling system of most impurities I would use the slow water change out method.
Open up the radiator drain valve all the way.
Open the fill cap.
Let the radiator drain until empty then close the valve and refill with water.
Replace the fill cap.
Start the engine and let run until normal operating temps are reached then shut off and let cool for 10 min.
Drain the radiator again, then refill with water.
Start the engine and let run until normal operating temps are reached then shut off and let cool for 10 min.
Drain the radiator again, then refill with water.
Start the engine and let run until normal operating temps are reached then shut off and let cool for 10 min.
You get the idea here, do this 5 times.
Then drain the radiator one last time and add 100% coolant, read the container and make sure it is not the 50/50 water/coolant mix.

DO NOT open the radiator drain valve and put the hose in the radiator and fill with fresh water and just let the engine run or you may blow a head gasket.
Patience is the key here you don't need to get in a hurry and risk damaging your engine.