Stretch out alone: get sloshed (8)
I believe the answer is:
elongate
'stretch out' is the definition.
(to elongate is to stretch or extend)
'alone get sloshed' is the wordplay.
'sloshed' indicates anagramming the letters.
'alone'+'get'='aloneget'
'aloneget' with letters rearranged gives 'ELONGATE'.
(Other definitions for elongate that I've seen before include "Stretch, lengthen" , "Spread" , "Open out" , "Make longer" , "Gone late oddly to extend" .)