Drain pipe fitted to vehicle (7)
I believe the answer is:
exhaust
'drain' is the definition.
(exhausting is a kind of draining)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for exhaust that I've seen before include "part of car - > tire?" , "Car's fume pipe" , "Pipe that carries engine fumes away" , "Car part for carrying away gases - would make you tired" , "Drain completely" .)