FWIW: The reason I wouldn't store crushed coral is that even after cleaning it, I'd want to rinse it before I used it anyway. Even stored well, I'd be concerned about dust or fungus, and would therefore insist on cleaning it again before puttin it in any tank. Of course I wouldn't want to store it without cleaning it, since that would be begging for problems. Rather than deal with cleaning it twice (before storage and before use), I'd just buy new and only clean it once, before use.
For using oxyclean: determine roughly how many gallons of water you'll need to completely submerge the CC, plus a little. Add one scoop (about 1 tablespoon) per gallon of hotwater, stir to dissolve. Add CC, stir. Let soak til water cools. Rinse well.