S.H.
Do you mean for brushing teeth? For my daughter, I'd give her a little cup of water, tell her to take a sip but don't swallow it, and then spit it out in the sink. I'd do it with her so she could watch. It took her a few tries to get it because she would accidentally swallow the water first! haha But she'll be 4 years old in a few days and she handles that part of brushing teeth pretty well. She knows not to swallow the toothpaste while brushing, and then she'll sip water & spit into the sink several times. They just need to practice!