what's your medium? and size of pot? if you regularly variate between water and fert, you shouldn't need to. always use an EC meter when watering. i check my runoff with an EC every single time. that tells me exactly how much salt is in my medium. check your ec going in, then check it coming out. measure the gain or loss. if it goes up, time to flush, depending on the amount it went up. just some RO water might be all you need. if it stays the same, you're cool, no need to flush yet. as long as you're in you're proper EC range.
I do, but have only ever uses straight water, I just keep pouring 3 gallon buckets of water over them. Stop for awhile and flush another 6 gallons thru the. I always put them back under he light to allow the soil to dry out good.