1991 240sx: Proper procedure for flushing radiator.

[vancouverbc]

The factory service manual details how to do it but they never mention that you have to close the petcock(drain) on the radiator at any point which makes things ambiguous. They clearly say to tighten the the drain plug on engine block after draining coolant and before flushing. I assume that you are running the engine while you put water in for the flush. My main concern is that you wont drain all the water with the drain plug on engine block closed. I assume the water is circulating with engine on and drains through the radiator drain? Chilton mentions to use a steady supply of water from garden hose.