I do a regeneration so I dont bother to flush at all...I just add water and/or nutes to keep the ppm at 900 and ph at 5.5-5.8...
I use GH nutes 3 part flora series and omit the grow component altogether, use 8 ml micro and 16 ml bloom in each gallon of reverse osmosis (deionized) water, called the Lucas Formula...
I am on re-generation 4 now and my girl Snow White is just getting better each gen...I'm not sure this would be possible in soil, not enuf control of nutes I'd figger, but once you get it down, maybe even dirt farmers could do a regeneration ...