Washout is basically twisting the wing so that the wing tip is at a lower angle of attack (AOA) than the root of the wing. This causes the root to stall first. It helps during landings, but it also helps any time you starting messing around near the "critical AOA", which is the AOA where the wing stalls. Washing is frequently used to tame a plane that has a bad snapping tendancy.

In practice, you can SOMETIMES add more up elevator once you reflex the ailerons. However, you don't necessarily get a tighter turn or loop. After all, the elevator is basically increaseing the wing's AOA, while reflexing the ailerons lowers it. And a lot depends on the particulars of the plane of course. Some airfoils really don't like reflexed ailerons, others seem to fly better with a little reflex. Also, the more tapered the wing (again, assuming non-tapered ailerons), the more washout effect you get with you reflex.

Basically, I'd say fly the plane, then add a little bit of reflex and fly it again and see if you like the performace better. If you don't, take the reflex out. It's easy to adjust, after all.

Another thing you can try if you want to tame a bad snapping tendancy is stall strips on the wing root area.

Oh, and if you haven't already, check your lateral balance. An unbalanced plane will snap more than one in balance. Does your plane always snap in the same direction, or does it snap both ways roughly the same? And if you haven't sealed the aileron hinge gaps, that can help as well.