Larry's correct.
When finished a Teaspoon of Baking Soda is good 'insurnace' to make sure the water/flushing agents (remaining) are totally non-corrosive.
After driving a few weeks, drain it again & add Coolant if wanted/needed.
In the California desert most run 100% coolant. If there's a need (on the road) to add water your still protected from freezing etc.
Happy trails.
