Words sent to me in a PM by someone very knowledgeable on the subject, I don't know if he would want me to mention him by name but I also don't want to take the credit.
"Personally I have no faith in flush kits and have yet to see any documented evidence they do anything other than lighten your wallet. The 4:1 waste ratio when the unit is in operation should be sufficient. They can't hurt anything though I suppose."
i have my ro under my kitchen sink and i have never flushed it or know how or even knew u had too..... well mine has a shut of valve on the blue line and not on the waste part. I was wondering if a shut off is need on the waste line as well...