You might want to skip the flushing step. Flushing has become such an ingrained part of marijuana growing lore for so many years now and there will be a number of people who disagree with what I say here. Cannabis is a hyperaccumulator plant and countless studies have shown that no amount of flushing will rid plant tissue of stored nutrient or toxin accumulation. Hemp is so good at storing toxins it's often used to help clean up contaminated areas where toxic chemicals have leeched into soil. I've had dozens of folks tell me all about the benefits of flushing my grows and on the surface it seemed to make sense until you look at the actual science of it. If you'd like to see any of the study data, I'd be happy to share links with you. As far as your yellowing leaves go, you might want to remove them to allow more light and air into the interior. You've got a great looking grow going. Congratulations!