I'm not sure exactly what your asking, if you mean how do you move the plant with it grown through the screen then your going to need to attach the scrog screen to your buckets, here's some DIY portable SCROG screen threads:
(-->CLICK HERE<--) (-->CLICK HERE<--) As for flushing/draining, well that will depend on your setup, your budget and your preference, there are many ways to achieve drainage, flushing is just basically rinsing the soil with fresh PH'd water to remove the built up salts, there's really only one way to do it, poor a couple gallons of fresh PH'd water through the soil. For some reason I think I misunderstood your question, did I miss something?