Barrel tax (3)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
vat
This clue is a double definition.
'barrel' is the first definition.
(a vat is a large tub or barrel)
'tax' is the second definition.
(UK Value Added Tax)
(Other definitions for vat that I've seen before include "Large tank or vessel" , "Large container for liquid" , "Fermentation vessel" , "Large tub; tax" , "Container for liquids" .)