Drain pipe? (7)
I believe the answer is:
exhaust
I believe this is a double definition.
'drain' is the first definition.
(exhausting is a kind of draining)
'pipe?' is the second definition.
(exhaust pipe is a kind of pipe)
(Other definitions for exhaust that I've seen before include "Burnt gases are discharged here" , "Completely tire out" , "Car part for carrying away gases - would make you tired" , "Pipe that carries engine fumes away" , "Deplete" .)