Main pressure around municipality's first sewer (10)
I believe the answer is:
seamstress
'sewer' is the definition.
(someone who sews)
'main pressure around municipality's first' is the wordplay.
'main' becomes 'sea' (the main is an old name for the sea).
'pressure' becomes 'stress' (I've seen this in another clue).
'around' means one lot of letters goes inside another.
'municipality's first' becomes 'm' (sst letter of 'municipality').
'sea'+'stress'='seastress'
'seastress' going around 'm' is 'SEAMSTRESS'.
(Other definitions for seamstress that I've seen before include "Midinette" , "Dressmaker" , "needlewoman" , "Woman who sews for a living" , "sewer" .)