Water down cement mix used by inspector (6)
I believe the answer is:
dilute
'water down' is the definition.
(I've seen this in another clue)
'cement mix used by inspector' is the wordplay.
'cement mix' becomes 'lute' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'used by' is a charade indicator (letters next to each other).
'inspector' becomes 'di' (abbreviation for Detective Inspector).
'lute' put after 'di' is 'DILUTE'.
Can you help me to learn more?
(Other definitions for dilute that I've seen before include "Weaken by adding water" , "Lessen the strength of a solution" , "lost concentration" , "Adulterate" , "The time when something ceases to have validity" .)