Deplete (7)
I believe the answer is:
exhaust
'deplete' is the definition.
(I know that deplete can be written as exhaust)
This is all the clue.
(Other definitions for exhaust that I've seen before include "Burnt gases are discharged here" , "Empty" , "Car's waste gas" , "Tube carrying off fumes from car engine" , "Completely tire out" .)