Knight led astray, taking drugs in sewer (6)
I believe the answer is:
needle
'sewer' is the definition.
(I've seen this before)
'knight led astray taking drugs' is the wordplay.
'knight' becomes 'N' (chess abbreviation).
'astray' indicates anagramming the letters.
'taking' is an insertion indicator.
'drugs' becomes 'ee' (an abbreviation for ecstasy written twice).
'led' with letters rearranged gives 'dle'.
'dle' enclosing 'ee' is 'eedle'.
'n'+'eedle'='NEEDLE'
'in' acts as a link.
(Other definitions for needle that I've seen before include "joint" , "Annoy - bodkin" , "Bug" , "It's vital to baste" , "Pin" .)