Where sink contains sticky stuff (5)
I believe the answer is:
resin
'sticky stuff' is the definition.
(sticky substance)
'where sink contains' is the wordplay.
'contains' indicates the answer is hidden within the clue.
'RESIN' is hidden within 'where sink'.
(Other definitions for resin that I've seen before include "Synthetic substance" , "Sticky stuff as from pine tree" , "Risen (anag.)" , "Origin of amber" , "It's obtained from tree-sap" .)