To give oral sex to either a man or a woman.
He gave me a suck down last night.
She gave Gary a suck down in the car at the drive-in.
To smoke a bong.
"Keen to go back to my hut and suck down some bong's."
"Nah, Let's go suck some down at my joint."
"Hey brother, hurry up and suck down that cone."