May well be bent over the sink (4)
I believe the answer is:
taps
'sink' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'may well be bent over' is the wordplay.
'may' becomes 't' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'well' becomes 'spa' (both can mean a spring or water source).
'be bent over' shows that the letters should be reversed in order.
'spa' written backwards gives 'aps'.
't'+'aps'='TAPS'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for taps that I've seen before include "Knocks gently" , "Exploits" , "pierces" , "Strikes lightly; eavesdropping devices" , "Bugs (wire)" .)