If you find yourself overfilling often, or if you are in the business and do heavy line work like I did (engine/transmission replacements and overhauls), just save yourself the time and get a fluid evacuator. If you overfill something you can pump a bit back out, they make them with pneumatic attachments or with a handpump that looks a bit like a bicycle tire air pump. Shove the little feed tube down the dipstick and pump whatever you need to back out.