There is a drain valve near the lower hose to the radiator. Put a clean pan under there and drain until nothing else comes out with the radiator cap off. Let it drain a little longer to let some more coolant work it's way out of the engine.
At that point, it should be low enough, that you at least won't make too much of a mess. When I reuse coolant that I have drained, I put a cloth in a funnel as I pur the coolant back in to strain out anything that might have fallen in the drain pan.