If you're using synthetic fertilizer you want to flush during the final 2 weeks of the plants life. If you're using organic fertilizer you really don't need to flush at all. You flush with plain ph'd water and usually with 3x the size of the container. So if you have a 3 gallon put you flush with 9 gallons of water.
Organic fertilizers don't need flushing? Do you think the plant can tell the difference between man made and organic particles? It does not matter what you use you still need to remove the active ingredients remainng in the plants make up. Using straight water you should flush daily for 7-10 days for medicinal grade, using a min of twice as much liquid as yu sually use to feed. Growing in soil requires addtional flushing.
Do you think the plant can tell the difference between man made and organic particles?
Synthetic fertilizers have more salt in them than organic fertilizer. If you're trying to get all the chlorophyll out that's another story, although I don't see that point of that since the plants need it.