Clean up the fourth city (3,4)
I believe the answer is:
tel aviv
'city' is the definition.
(Israeli city)
'clean up the fourth' is the wordplay.
'clean' becomes 'valet' (valet can mean to clean).
'up' is a reversal indicator (in down clue: letters go upwards).
'the fourth' becomes 'iv' (Roman numerals for four).
'valet' back-to-front is 'telav'.
'telav'+'iv'='TEL AVIV'
(Other definitions for tel aviv that I've seen before include "Second largest city of Israel" , "city on the Mediterranean coast" , "Major city of Israel" , "Financial centre of Israel" , "Evil Vat imposed on Israeli city" .)