The abstainer takes nothing in but a little rum! (3)
I believe the answer is:
tot
'but a little rum' is the definition.
I can't judge whether this defines the answer.
'the abstainer takes nothing' is the wordplay.
'the abstainer' becomes 'tt' (I've seen this in other clues).
'takes' is an insertion indicator.
'nothing' becomes 'O' (O resembles 0).
'tt' placed around 'o' is 'TOT'.
'in' is the link.
Can you help me to learn more?
(Other definitions for tot that I've seen before include "Small baby" , "Arithmetic for infant" , "Small drink of spirits" , "quick drink" , "Spirit measure" .)