Large tank destroying megastore (9)
I believe the answer is:
gasometer
'large tank' is the definition.
'destroying megastore' is the wordplay.
'destroying' indicates anagramming the letters.
'megastore' with letters rearranged gives 'GASOMETER'.
(Other definitions for gasometer that I've seen before include "Fuel storage tank" , "Game store (anag) - fuel store" , "source of fuel" , "Large fuel tank" , "could be seen by the Oval" .)