Clean city below (7)
I believe the answer is:
launder
'clean' is the definition.
(laundering is a kind of cleaning)
'city below' is the wordplay.
'city' becomes 'la' (Los Angeles).
'below' becomes 'under' ('under' can be a synonym of 'below').
'la'+'under'='LAUNDER'
(Other definitions for launder that I've seen before include "Cleanse (material or money)" , "Clean, clothes or mafia money" , "Led a run (anag)" , "Perhaps decriminalise" , "Make illegal (money) legitimate" .)