It shouldn't matter, but it's best to use a special feeding cup to prevent pollution and keep it clean.

You can go to a Buddhist shop and buy a small cup with "Monk" printed on it. Just the right size (that is, the cup in Haitao video, which is usually used to hold nectar before Buddha). I bought a plastic spray emulsion that can be sprayed in jewelry stores, which is more convenient when I go out to eat.