I have tried both ways.

And to be honest I found in (PROMIX)

One plant I flushed 2 weeks proir to harvest with just plain water. And continued to feed just plain water untill harvest.

the other plant I used a Solution 1 WEEK before harvest then continued to use just water untill harvest.

And the one that I used the solution in tasted much better. So for 10 bucks for some solution it was worth it for me cuz I can feed my plant with nutes for longer. and It tasted better when smoked.

Rember your Not just flushing the PLants soil out, but rather starving the plant of nutrients to force the plant to use what nutes it has left in its leafs etc. Because nasty tasting weed is usually the result of Nitrogen and toxic nutes still being present in the Leafs and buds, (Or so I have read)

good luck

kd