I use a flushing agent, but that's $20 per gallon sugar water. Research a little and you should be able to find how to make your own, if you're into that. The last week to 10 days should get nothing but water or water with a flushing agent.

On the other hand, I've had many people ooh and awe over my harvests that have never been flushed. A lot probably depends on what chemicals she's eating near the end. Organic shit normally tastes less... shitty.