Make good business, plugging pure rubbish (6)
I believe the answer is:
recoup
'make good' is the definition.
(synonyms)
'business plugging pure rubbish' is the wordplay.
'business' becomes 'co' (short for company).
'plugging' indicates putting letters inside (inserted letters plug up a gap in the word).
'rubbish' indicates anagramming the letters (a poor quality or rubbish spelling of the letters).
'pure' anagrammed gives 'reup'.
'co' placed into 'reup' is 'RECOUP'.
(Other definitions for recoup that I've seen before include "Regain (expenditure)" , "Regain (something lost)" , "Get back, say expenses" , "make good one's losses" , "Regain a loss through subsequent profits" .)