Tank (3)
'tank' is the definition.
(type of container)
This is the entire clue.
(Other definitions for vat that I've seen before include "Large barrel" , "A tax on a large container?" , "possible source of liquid" , "Large tank; purchase tax" , "Container for liquids" .)
'tank' is the definition.
(I know that cistern is a type of tank)
This is all the clue.
(Other definitions for cistern that I've seen before include "Water container" , "WC water tank" , "Tank - sac of body fluid" , "bit of toilet" , "Toilet tank [ital]" .)