When you get a new unit, you should flush off or run about 3 gallons of water through the system. This is to remove any carbon fines and preservatives off of the RO membrane. If you have the fast flush and/or DI Bypass valves, open them for the flush. On a new unit, remember to flush for 3 gallons or one hour (which ever comes first/easiest is fine). After installing new filters (excluding the RO membrane), a good 5-15 minute flush is fine. If you install a new membrane, a good 30 minute flush is needed.