a commonly acceptable procedure is -
- open the drain plug
- plug in a garden hose on the rad inlet. let water run.
- start engine
- run on idle for 5-10 minutes
- shut engine off
- stop water
- open dran plug and let rad run empty
- close drain plug
- fill up distilled water
- start and let engine run for a minute or so
- open drain plug
- repeat "fill distilled water - start engin - drain plug"
- final close drain plug
- final fill distilled water
