Am I a plumber now? lol. You know my take on flushing, it's for toilets.
When ripening plants I am a believer of a proper ripening feed. Low in Nitrogen, but still plenty of potassium, sulfur and such as these are key for terpene building. We want really terpy bud. Flushing the plants with plain water, especially in hydro, will starve your plant of key elements during the most important time in it's life, ripening. We don't want to do all this work growing a plant and then yank the rug out from under it at the end.
My ripening feed would be a lower PPM than my mid flower feed. I feed all the way to the chop.
Some elements we wish to have present for terpene production:
Potassium
Sulfur (this is very much a valued element)
Chlorine (small amounts of chlorine go a long ways for terpene production, Potassium Chloride is my friend, two elements for the price of one lol)
Elements that you want to avoid having in quantity during ripening would include Nitrogen and Phosphorous. These can cause harsh flower, this is what we want to avoid. Too much nitrogen can also promote fox tailing during later flower.
There are a million different ways to grow weed, this is mine and it has served me well. The few times I have tried flushing I was less than pleased.