Sewer in the main street runs with muck outside (10)
I believe the answer is:
seamstress
'sewer' is the definition.
(someone who sews)
'main street runs with muck outside' is the wordplay.
I cannot quite understand how this works, but
'main' could be 'sea' (the main is an old name for the sea) and 'sea' is present in the answer.
'street' could be 'st' and 'st' is found within the answer.
'runs' could be 'r' (cricket abbreviation) and 'r' is present in the answer.
The remaining letters 'mess' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'in the' acts as a link.
(Other definitions for seamstress that I've seen before include "needlewoman" , "sewer" , "Dressmaker" , "Woman who sews for a living" , "Midinette" .)