Fastener in sink's tap leaks (6)

I believe the answer is:

staple

'fastener' is the definition.
(staple is a kind of fastener)

'in sink's tap leaks' is the wordplay.
'in' says the answer is hidden in the clue.
'STAPLE' is hidden in the letters of 'sinks tap leaks'.

(Other definitions for staple that I've seen before include "Principle - metal fastener" , "security device" , "standard" , "key" , "Paper fastening" .)

I've seen this clue in The Telegraph.

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