Rush to get mug in seaside location (9)
I believe the answer is:
dartmouth
'seaside location' is the definition.
'rush to get mug' is the wordplay.
'rush' becomes 'dart' (darting is a kind of rushing**).
'to get' says to put letters next to each other.
'mug' becomes 'mouth' (slang term).
'dart'+'mouth'='DARTMOUTH'
'in' is the link.
(Other definitions for dartmouth that I've seen before include "Devon town" , "Devon resort" , "Location of Britannia Royal Naval College" , "port" .)