depends on the reason you are flushing if flushing due to nute burn, simply run water thru your pot 2-3x the size of the pot. i.e. 3 gallon pot, "flush" with 9 gallons of ph'd water if flushing at the end of cycle you simply want to cut off any added nutes and just feed water for 1-2 weeks before harvest also, you're in the wrong section but question has been answered anyway