When I looked up the word "suck" in my dictionary,
some of the example sentences use the preposition "at" after suck and some don't.
Why and what's the rule?
The example sentences are:
You can't get a good suck at a drink if the straw is damaged.
Th baby was sucking at his mother's breast.
She sucked the orange dry.
He sucked at his pipe.
Suck a lozenge for your sore throat.
The child sucked her thumb.