All I do to flush out old radiators is use a fitting that I made up to hook a garden hose to one side and a drain valve on the other. Fill up the radiator with the garden hose, leaving the drain valve open at first, to flush out the really large chunks and then close the drain and let the radiator pressurize to hose pressure. You can vent out the air with the vent valve on top. This not only flushs out the radiator but gives it a good pressure test as well. I then open the drain valve and let it flow until it runs clean. Then drain and install.