Academic gets important job, but it's drudgery (6,4)
I believe the answer is:
donkey work
'it's drudgery' is the definition.
(I've seen this before)
'academic gets important job' is the wordplay.
'academic' becomes 'don' (type of academic - especially at Oxbridge).
'gets' says to put letters next to each other.
'important' becomes 'key' (similar in meaning).
'job' becomes 'work' (synonyms).
'don'+'key'+'work'='DONKEY-WORK'
'but' acts as a link.
(Other definitions for donkey work that I've seen before include "Grind" , "Drudgery" , "A lot of effort" , "chore" , "Carrying children on the beach" .)