All good advice.

I flush regularly during the course of growing. It removes the buildup of salts and other bad stuff in the soil. I have flowerpots about 11" tall and 11" across. I pour water in for a long ten-count and let it drain through as I do the same for the other plants. Then I do it all again x3. I have those big tin foil turkey pans under the flowerpots to catch all the water, and I suck the water out of them with a hand bilge pump. I'd imagine it's about 2gal/pot/flush. I flush about every 4-6 weeks, making sure I do it before any change of lighting or nute formula. So I'd do it a couple times during veg, once before kicking the lights down, again before kicking them into bud, and finally a week or so before harvesting.

If you flush, it's important to get rid of the excess water immediately, and also to wait until the soil is pretty dry before watering again. Pot is a desert weed and likes things on the dry side. HAving them sit in standing, staganant water or over-damp soil will cause more problems than i care to list here.