I posted this before on numerous occasions, so I'll just copy and paste it here for you.
"I was gonna write that this info I'm giving you was "my opinion", but it's not my opinion, it's a fact. You don't need to flush your plant to get great tasting, super smooth smoke from your plant. I myself, along with NUMEROUS, other long time, extremely knowledgable growers on this site(and other sites also), NEVER, EVER flush. As long as you dry your buds right, and then cure them right, you'll have the best smoke you've ever packed in your bowl. In fact, I'll even go as far as to say that if you do flush, your plants will take longer to finish up. Here's the way I see it. The one time I flushed my plant(b4 RIU existed, when I was a noobie, and went by what some others said), my plant seemed to suffer more than anything. It started to droop, and the leaves all started turning yellow. Yes, some leaves will die and turn yellow towards the end of flowering, but not like mine did and expeditiously following the flush. A flowering plant needs food to produce the biggest, bestest buds possible, especially in the end when it's finishing up. If you strip the grow medium of the essential nutrients that your plant is using, it's gonna suffer. No two ways about it. I feed my plants right up to a week before harvest, and I've been told on more than 100 occasions, lol, that my stuff is the smoothest they've ever had. I've done the test to see if there was a difference, and there wasn't. Flushed one plant(same strain and grow times, etc.) and left the other one alone, and you would never be able to tell the difference between the two."