Petrol container in Sherman say (4)

I believe the answer is:

tank

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'petrol container' is the definition.
'tank' can be an answer for 'container' (tank is a kind of container). I am not sure about the 'petrol' bit.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for tank that I've seen before include "Military machine" , "Vat" , "Miltary vehicle" , "Container for liquids - military vehicle" , "A military vehicle or large container" .)

I've seen this clue in The Sun.

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