I have seen grows with planters with NO DRAIN HOLES using organic soil, the grower just water/fertilized just enough each time. Of course the guy was a master grower.

I have drain holes and trays myself. Best case scenario in a grow to me would be to flush at the very last watering before harvest (never been able to time it like that though). When I say "flush" I mean drain the water from the trays, as in the volume of the pot in water. Example a three gallon pot with soil, roots, and plant would be flushed with three gallons of water (or more).
Basically I only flush when I make a mistake or at the end of a grow. Some organic gardeners don't flush at all. Many different schools of thought out there. Had to harvest early this grow, no flush, some black ash and "sizzling" but the taste is there and it's not harsh. Whould have been a lot worse if I had used chemical fertilizers, almost unsmoke able.
Peace out.