Flush is such a 'gross' word. Let's call it "ripen on the vine".
I never give plain water, almost never. it's always got something in it, because my soil always has something in it, and the plant wants 'something' at every point in its life. even as it is dying, it needs stuff to make sure seeds are ripe, and buds are fat.
So, if you are in soil, the later it gets, the more facilitators are used, and less of the actual nutrients by the grower. Adding enzymes, microbes, and the like will enable the plant to 'ripen'. the plant is a living being, it does not want to be FLUSHED.
.02