Pots of gravy in bottomless trousers (4,7)

I believe the answer is:

deep pockets

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'pots of gravy' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.

'bottomless trousers' is the wordplay.
'bottomless' becomes 'deep' (similar in meaning).
'trousers' becomes 'pockets' (I've seen this before).
'deep'+'pockets'='DEEP POCKETS'

'in' is the link.

Can you help me to learn more?

I've seen this clue in The Guardian.

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