Garage where favourite composer, leaving hydrogen, fills quota (6,7)
I believe the answer is:
petrol station
'garage' is the definition.
'favourite composer leaving hydrogen fills quota' is the wordplay.
I cannot really see how this works, but
'favourite' could be 'pet' (synonyms) and 'pet' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
'where' acts as a link.
Can you help me to learn more?
(Other definitions for petrol station that I've seen before include "Place to fill the tank" , "Filling up location?" , "Fuel supplier" .)