Ok so ask most and they will say three times the pot size is a basic flush, to clear the soil it would be water at pH6.5 till runoff was 6.5 approx. You see how without the nutes the soil will return to its or close to original pH.
Is the point to drain out the nutes for a cleare smoke? Great question, others may differ but here is my opinion - If you havent overfertilized the plant during flowering the bud will smoke and taste great once dried. The nutrients in the bud are already ingrained there when the bud formed so you cannot clear the bud of nutrients only the soil to some extent meaning the plant will consume some of its stored nutrients in order to survive and finish. Overfertilization will accumulate metal and nutrient ions in the leaves and buds, until the plant has dealt with these the bud will smoke harshly Properly grown weed that hasnt been overfertilized will taste great with or without a flush.-
Id just wait till the soil goes dry and needs a water again before adding more or you run the risk of overwatering and poor growth. Simply let the plant finish a few days later than you planned and allow a second decent flush a few days before harvest.
I sumise that the point of seeing a slight deficiency at the end of flowering is so you know the plant is just about using up the nutes you gave it and with just plain water in the last week to ten days a slight deficiency will occur. This is different to those who run a major Nitrogen deficiency through most of the flowering period and finish with mainly yellow or no leaves at all.
The proof is always in the smoking dude. Peace
