Cheers -- one guzzling wallop in South Seas location (6)
I believe the answer is:
tahiti
'south seas location' is the definition.
(Tahiti is an island of the Pacific)
'cheers one guzzling wallop' is the wordplay.
'cheers' becomes 'ta' (both can informally mean thank you).
'one' becomes 'I' (Roman numeral).
'guzzling' is an insertion indicator (I've seen this in other clues).
'wallop' becomes 'hit' (I've seen this in another clue).
'ta'+'i'='tai'
'tai' going around 'hit' is 'TAHITI'.
'in' is the link.
(Other definitions for tahiti that I've seen before include "Island in South Pacific, chief town Papeete" , "Pacific island, Gauguin's home in the 1890s" , "French Polynesian island" , "Windward island" , "Polynesian island where Gauguin lived" .)