Classifies as drunk son swallowing last of beer ... (5)
I believe the answer is:
sorts
'classifies' is the definition.
('sort' can be a synonym of 'classify')
'drunk son swallowing last of beer' is the wordplay.
'drunk' becomes 'sot' (both can mean someone who drinks too much).
'son' becomes 's' (genealogical abbreviation for son).
'swallowing' means one lot of letters goes inside another.
'last of' suggests the final letters.
The last letter of 'beer' is 'r'.
'sot'+'s'='sots'
'sots' placed around 'r' is 'SORTS'.
'as' is the link.
(Other definitions for sorts that I've seen before include "Arranges in different groups" , "Systematically arranges" , "classes" , "Arranges in correct or desired sequence" , "Categories" .)