Real Dictionary

suck
passive verb: If you are sucked into a bad situation, you are unable to prevent yourself from becoming involved in it.
verb: If something sucks a liquid, gas, or object in a particular direction, it draws it there with a powerful force.
verb: If you suck something, you hold it in your mouth and pull at it with the muscles in your cheeks and tongue, for example in order to get liquid out of it.

suck in American English
to draw (liquid) into the mouth by creating a vacuum or partial vacuum with the lips, cheeks, and tongue
intransitive verb: to draw something in by producing a partial vacuum in the mouth, esp. to draw milk from the breast
transitive verb: to draw into the mouth by producing a partial vacuum by action of the lips and tongue

suck in British English
verb: to draw (a liquid or other substance) into the mouth by creating a partial vacuum in the mouth