Brewery tub (3)
I believe the answer is:
vat
'brewery tub' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for vat that I've seen before include "Large tank; purchase tax" , "possible source of liquid" , "Barrel - tax" , "Large vessel for storing liquids and a large tax" , "Large tank for liquids, or kind of tax" .)