Bung in favourable publicity (4)
I believe the answer is:
plug
I believe this is a double definition.
'bung' is the first definition.
(thesaurus)
'favourable publicity' is the second definition.
'in' is the link.
(Other definitions for plug that I've seen before include "quid" , "Fitment at the end of a flex" , "Cork" , "Seal" , "Stopper - publicise" .)