Green’s Dictionary of Slang

1. (US campus) to finish off a drink, to empty a glass.

1865		Paisley Herald 9 Sept. 6/4: The Noble Grand [...] had been engaged in ‘bottoming’ a pot of porter.
1901		J. Caminada Twenty-Five Years of Detective Life II 60: He bottomed the glass, and his youthful friend ordered it to be replenished.
1989		P. Munro Sl. U. 44: Bottom it and we’ll go.

2. (Aus.) to bet all one’s money.

1901		‘Rolf Boldrewood’ In Bad Company 148: Every passing traveller [...] had nuggets of gold in his pocket, ‘or knowed a party as bottomed last week to the tune of £1200 a man’.
1936		‘Banjo’ Paterson Shearer’s Colt 127: We’d laugh our heads off if we left a goldmine behind us and went away and bottomed on a duffer.

3. to have sexual intercourse.

2005

G. Pelecanos Drama City 108: I bottomed her ass right there on the asphalt.

4. to assume the passive role in homosexual anal intercourse.

2013

NSFWCorp 5 June 🌐 Tony[...] finally pipes up between reps. ‘Actually, I like anal because it’s so personal.’ [...] (I later found out that Tony used to bottom in gay porn.