Forget flushing dude, you're growing in soil. You can't flush soil anyway. What people are getting at by the term flush here, is a couple of weeks before your chop date, just start feeding your plant with plain water only until runoff, not adding any nutes. This will make the plant use whatever is left in the soil or within itself. And hopefully give a better taste.
So you can forget about flushing until you've got to the end of flowering. The only time i would actually flush the soil ( as in, put alot of plain water through the pot and let it run away) is if i overfed the plant or was having ph issues.