Dan must work as a collector (7)
I believe the answer is:
dustman
'a collector' is the definition.
(I've seen this before)
'dan must work' is the wordplay.
'work' is an anagram indicator.
'dan'+'must'='danmust'
'danmust' is an anagram of 'DUSTMAN'.
'as' acts as a link.
(Other definitions for dustman that I've seen before include "Refuse worker" , "My old man's occupation" , "Refuse collector" , "Bin emptier" , "Rubbish collector" .)