dunk in(to) (something)
To push someone or something into a liquid. A noun or pronoun can be used between "dunk" and "into." Being nice to your little brother does not include dunking him into the pool, OK? I can't eat French fries without dunking them in ketchup first.
dunk someone or something into something
and dunk someone or something into submerge someone or something in something, fully or partially. They dunked him into the pool as a way of celebrating. Liz pulled the cup of coffee toward herself and dunked in her doughnut. She dunked herself into the cold water for just a minute.