Smoke getting fag out (7)
I believe the answer is:
exhaust
This clue is a triple definition!
'smoke' is the first definition.
(thesaurus)
'getting' is a link.
'fag' is the second definition.
(exhausting is a kind of fagging)
'out' is the third definition.
(thesaurus)
(Other definitions for exhaust that I've seen before include "Wear, tire out" , "Completely tire out" , "Pipe that carries engine fumes away" , "Tire out - waste gases from engine" , "Sap - piped emission" .)