Bum drink for your health! (7,2)
I believe the answer is:
bottoms up
'your health' is the definition.
(I've seen this before)
'bum drink' is the wordplay.
'bum' becomes 'bottom' (bum can informally mean one's bottom).
'drink' becomes 'sup' (to sup is to drink).
'bottom'+'sup'='BOTTOMS UP'
'for' is the link.
(Other definitions for bottoms up that I've seen before include "Down the hatch!" , "Toast" , "Cheers!" , "down it goes!" , "Your good health!" .)