Bull and pig clean (7)
I believe the answer is:
hogwash
'bull' is the definition.
(synonyms)
'pig clean' is the wordplay.
'pig' becomes 'hog' (synonyms).
'clean' becomes 'wash' (washing is a kind of cleaning).
'hog'+'wash'='HOGWASH'
'and' acts as a link.
(Other definitions for hogwash that I've seen before include "Baloney" , "bull" , "Bunk" , "Utter rubbish" , "Pig food" .)