Are you talking about flushing as in cleaning out the system or flushing the plants?
I was doing regular cleaning every few weeks... Just by flushing hot water through the lines (not connected to the autopots/valves obviously) and scrubbing the aquavalves with a toothbrush, as well as rinsing out the res before each fill-up... If you're using Drip Clean from the start you may not have to do any maintenance however, or maybe just once between grows... That's what I'm hoping at least for my next run since I've picked up a bottle of that as well.