Last drink? Down the hatch! (7,2)
I believe the answer is:
bottoms up
'down the hatch' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'last drink?' is the wordplay.
'last' becomes 'bottom' (eg at the bottom of a list).
'drink?' becomes 'sup' (to sup is to drink).
'bottom'+'sup'='BOTTOMS UP'
Can you help me to learn more?
(Other definitions for bottoms up that I've seen before include "down it goes!" , "Down the hatch!" , "Your good health!" , "Cheers!" , "Toast" .)