To move liquid around in a container so that it makes noise.
Sloshing can make people think of spilling, messes, or fun.
Examples:
I slosh the water in the bucket.
The milk sloshes in the jug.
Don't slosh the soup out of the bowl!
The kids slosh the paint all over the paper.
The waves slosh against the side of the boat.
The water sloshes and splashes all over the place.