flaps perform the function of altering the airflow...creating lift. Washout ,on the other hand prevents the tip stall at a given speed,in relation to the root.It is a different effect.Washout allows the wing to regain controlled airflow,by preventing an uncontrolled spin,often generated by a tip stall. Try this link,as an explanation...since you dont seem to get it.
http://www.rcscalebuilder.com/tutori...ut/washout.pdf