Some rest you can get out with a knife at the opening, but not all.
ADD SOME MILK, shake it (it emulsifies because milk is already a water-fat emulsion), and pour in style using the cap hole, or drink straight from the bottle.
Mayo-milk – super-yummy! – And not just for bottle cleaning. Of course you can also do this for bottles that are not quite empty.
I would almost call mayo-milk a decent replacement for vanilla milk, because it tastes very rich, sweet and creamy.
Plus, if you care, it produces cleaner waste, because then you merely have to briefly flush it with water and it’s gonna be clean.
P.S.: Try to avoid mayo with E385 (EDTA). It’s not good. There are a few alternatives that somehow don’t require it. Even ones with oils that are said to spoil quicker. (I have seen a tube mayo based on only canola oil and it does not have such preservatives.)