Empty the sack (9)
I believe the answer is:
discharge
This clue is a double definition.
'empty' is the first definition.
(I know that empty can be written as discharge)
'sack' is the second definition.
(I know that sack can be written as discharge)
'the' is the link.
(Other definitions for discharge that I've seen before include "unload" , "let go" , "Sack or fire weapon" , "Acquit" , "cashier" .)