I use soil and i will tell you from years of experience that you should flush even if using organic methods!!! I use FloraNova Grow and Bloom plus other supplements in 7 gal pots, and grow the big plants 5 to 7 ft MTF Strain.
Using the flawless finish be sure to use just enough water/flush mix to get a good run off ( for my 7 gal pots that's about 1 and 1/2 gallons no more) most importantly drain off the excess do not let the pots sit in the run off. you will use the flawless finish only once.
Secondly when it dries use straight water i use well water which is 0 ppm's with out issues and again water till you get a good run off and drain that run off. I do this starting my last week of flowering cycle 7 days is the magic number of days for my set up to flush. I as well would like to point out that your dry and cure times will be shortened if you flush your soil. Good Luck with your grow