Work out when filling gone — empty? (7)
I believe the answer is:
disused
'empty?' is the definition.
(I've seen this before)
'work out when filling gone' is the wordplay.
'work out' becomes 'sus' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'when filling' is an insertion indicator.
'gone' becomes 'died' ('die' can be a synonym of 'go').
'sus' inserted inside 'died' is 'DISUSED'.
Can you help me to learn more?
(Other definitions for disused that I've seen before include "Derelict" , "Neglected" , "No longer observed or practised" , "empty" , "No longer of service" .)