Figuring out some way to make your watering/draining process streamlined saves a ton of headaches. This is mostly based on my little experience since I'm on my first grow, but I had to do one flushing to raise my pH.
That one flushing with 5 plants, however, was a total circus. I used a piece of pipe through the loops of the fabric pots for a handle, picked up the plant with one arm, and then pulled the full tray and replace it with the new one. Then, maneuvered the tray around and over the pots, all without spilling water.