Rialto's broken sewer (6)
I believe the answer is:
tailor
'sewer' is the definition.
(thesaurus)
'rialto's broken' is the wordplay.
'broken' indicates anagramming the letters.
'rialto' anagrammed gives 'TAILOR'.
(Other definitions for tailor that I've seen before include "One makes suits etc. to measure" , "follower of tinker" , "Clothes-maker" , "Maker of men's suits" , "Maker of fitted clothes" .)