When your plants have approx 95% brown pistils stop all nutrients, fertilizers and supplements and harvest about 2 weeks later once there are 98-99% brown pistils and your desired ripeness of the trichomes has occurred.
For "flushing", there is no need to drown your plants with gallons of water, just stop all additives and give only plain water, in normal amounts and at normal intervals and the plants will "flush" themselves naturally.
Drowning the plants with huge amounts of water will not make this occur any faster, the plants metabolism works at a certain pace and can not be accelerated with floods of water............it takes time, (roughly 10 days) for the plant to do this all by itself...........not huge amounts of water.