The general rule, as I see it mate, is if using organic feed don't worry, I've chopped with no flush and been fine. If chemical nutes, like plant magic soil grow then after the last feed, water it and let it dry at least. There's so many variables growing pot it's just impossible to call some things with a 100% guarantee. But I agree with that skeleton guy, there has been alot of effort gone into finding out if a flush matters or not.