Knocks lightly on the faucets (4)
I believe the answer is:
taps
'knocks lightly on the faucets' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for taps that I've seen before include "Military bugle call at dusk" , "The sound of lights out" , "Exploits" , "Military signal and faucets" , "Knocks lightly on the faucets" .)