Scientist off filling rubbish receptacle (6)
I believe the answer is:
boffin
'scientist' is the definition.
(boffin can informally mean a scientist)
'off filling rubbish receptacle' is the wordplay.
'filling' is an insertion indicator.
'rubbish receptacle' becomes 'bin' (rubbish bin).
'off' inserted inside 'bin' is 'BOFFIN'.
(Other definitions for boffin that I've seen before include "(Government) scientist" , "Back-room boy" , "Scientist (in the back room?)" , "Scientist (sl.)" , "Brainbox" .)