Green’s Dictionary of Slang

1. to leave, to finish.

1921		D.L. Sayers Unpleasantness at the Bellona Club (1977) 211: Perhaps I’d better poop off. So long.
1932		D.L. Sayers Have His Carcase 406: At the moment when everything is ready to poop off, the rest of the gang arrive.

2. (US) to spend.

1965		J. Thompson Texas by the Tail (1994) 72: Teddy was pooping off enormous amounts of money.
1966		‘Tom Pendleton’ Iron Orchard (1967) 83: What have you got to show for all the dough you’ve [...] pooped off once a year, going to New York?

3. see pop v.¹ (1b)