Hello cable24601,
Ron has not posted here in about two years, so I don't think he will be replying. I have not read anything (other than manufactures clams) that says that flushing before harvest improves anything. I do flush the system every time I change the
nutrients with fresh plain water though. That is to help flush away some of the
nutrient salts out of the
growing medium and system. If not, it could build up and cause nutrient lockout from toxic buildups.
But I have never read anything from a creditable source that supports flushing just before harvest for any reason. You want to keep nutrient lockout from happening thought the plants life, not just at the end.
P.S. When I say I flush the system, I am not meaning for days or even a 24 hour period (like some say to do before harvest). I clean the system out, then fill with just plain water, and run it through a couple of cycles. Then dump and repeat. If there is a lot of growing medium to flush, I may even do it 3 or 4 times. All in all, I probably only flush with plain water for between 2-4 hours before draining, and then adding the new nutrient solution.