Enquires after empty fuel bottles (6)
I believe the answer is:
flasks
'bottles' is the definition.
(flask is a kind of bottle)
'enquires after empty fuel' is the wordplay.
'enquires' becomes 'asks' ('ask' can be a synonym of 'enquire').
'after' is a charade indicator (letters next to each other).
'empty' suggests removing the centre.
'fuel' with its centre removed is 'fl'.
'asks' put after 'fl' is 'FLASKS'.
(Other definitions for flasks that I've seen before include "Bottles with narrow necks" , "Containers for liquid, thermos say" , "Narrow-necked bottles, may be of vacuum type" , "Glass containers" , "Narrow-necked bottles, thermos or vacuum" .)