That's a great question. I lifted the plant, rinsed the roots and tried to 'hydro' it for 3 days. Never again.Yeah, there is no need to flush if you're not adding nutrients.
I'm curious how you even flushed at all if you were only giving plain water?
I don't rinse copious amounts of water to leach the media, I just switch to plain water and feed as normal with the same minimal runoff and let the plant use up what is stored in the rootzone and plant tissues for the last week.
What a mistake. Flushing is almost impossible with an organic soil grow.