Former politician drowning in beer, for instance (7)
I believe the answer is:
example
'instance' is the definition.
('example' can be a synonym of 'instance')
'former politician drowning in beer' is the wordplay.
'former' becomes 'ex'.
'politician' becomes 'mp'.
'drowning in' means one lot of letters goes inside another.
'beer' becomes 'ale' (I've seen this before).
'mp' put into 'ale' is 'ample'.
'ex'+'ample'='EXAMPLE'
'for' is the link.
(Other definitions for example that I've seen before include "Something to be imitated" , "Something illustrating a general rule" , "Specimen, sample" , "Paradigm or model" , "warning" .)