Dump rotten cargo (7)
I believe the answer is:
offload
'dump' is the definition.
(I've seen this before)
'rotten cargo' is the wordplay.
'rotten' becomes 'off' (rotten food is 'off').
'cargo' becomes 'load' (synonyms).
'off'+'load'='OFFLOAD'
(Other definitions for offload that I've seen before include "deliver goods" , "Get rid of (unwanted item or burden)" , "9 [JETTISON]" , "Dump" .)