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.
EDIT: Fluid Evacuator
Its pretty unusual to have lube techs doing any diagnosis, but did she ask him if he likes chocolate milkshakes? Because That’s exactly what you create when you mix water in engine oil. Just don’t drink it.