China impounds contents of this vessel (5)
I believe the answer is:
phial
'vessel' is the definition.
(phial is a kind of vessel)
'china impounds contents of this' is the wordplay.
'china' becomes 'pal' (china plate is Cockney rhyming slang for mate).
'impounds' is an insertion indicator.
'contents of' says to take the centre (the letters on the inside of the word).
The centre of 'this' is 'hi'.
'pal' placed around 'hi' is 'PHIAL'.
(Other definitions for phial that I've seen before include "Small flask" , "Ampoule" , "glass container" , "little bottle" , "Source of medicine" .)