Flushing really needs to be done if you been fertilized still into flowering. A week before harvest just strait water. The dark thing unsure. If you find thread by budzbudda about soil setup it's a easy setup just need few things and only feed with liquid kelp every two weeks nothing else. So there's no need to flush. Living soil,has everything in bucket your plant needs through our whole grow. And add some soil to top dress every couple months. Kinda want it dry when harvest. When chopped Keeping it 60 ° and ideally 60 humidity. With fan blowing but not on them. Then cure for month won't taste as good just fresh dried bud.