WHEN I used to flush, I'd flush once, thoroughly, then switch to straight water, for the rest of ther grow, watering normally. But, now that I have a good grasp on feeding/nute useage, I don't flush anymore, I just switch to straight water, for the last week or so. I can't tell the difference, between flushing, and not flushing, as long as I haven't overfed them,(according to my own guidelines) in late flowering.