School to throw out drinker (3)
I believe the answer is:
sot
'drinker' is the definition.
(I know that sot is a type of drinker)
'school to throw out' is the wordplay.
'school' becomes 'S'.
'throw out' indicates an anagram.
'to' with letters rearranged gives 'ot'.
's'+'ot'='SOT'
(Other definitions for sot that I've seen before include "A chronic drinker" , "One's often intoxicated" , "Habitual drinker" , "One drinks" , "drunk" .)