Crustacea clean when cooked in pubs (9)
I believe the answer is:
barnacles
'crustacea' is the definition.
'clean when cooked in pubs' is the wordplay.
'when cooked' indicates anagramming the letters.
'in' is an insertion indicator.
'pubs' becomes 'bars' (I've seen this in other clues).
'clean' is an anagram of 'nacle'.
'nacle' put within 'bars' is 'BARNACLES'.
(Other definitions for barnacles that I've seen before include "crusty lodgers" , "Balancers for shellfish that stick to hulls" , "Geese" .)