Drain rad. Fill with it with distilled water. Run. Drain rad, Fill it with distilled water. Run. Drain rad ( the coolant expansion tank drains with the rad on the Burb) Fill rad with pure antifreeze. Fill coolant jug with 50/50 mixed antifreeze.Seems to come out close to 50/50. I did it twice on my 2008 Burb. ( once every 5 years, with 5 year Dex-cool) . Thirteen years old with 210,000 miles. Original rad and water pump.