Hey, I'm not KP but I will try to answer your questions. To flush, it doesn't really matter when you do it, just make sure you allow your pots to dry out completely before watering again in the future. And when you flush, to do it completely, flush with about 3x the amount of water your pot holds. ie. 3 gallon pot=flush with 9gallons of water. After you flush, i would follow up with lighter than full strength nutes.