Its not really needed when your using organics. If you've been adding pesticides or been going heavy with chemical nutrients then I'd stop feeding 2 weeks before, hold back on watering for a bit, then flush during the last week.
I stop nutes 2 weeks before harvest and flush 4-5 before. I do not water after the flush until 2 hours before harvest just to make it easier to trim.
Good luck. Pics?