Drink — it's knocked back by family member breaking into song (3,5)
I believe the answer is:
tia maria
'drink' is the definition.
(I know that Tia Maria is a Alcoholic beverage)
'it's knocked back by family member breaking into song' is the wordplay.
'knocked back' is a reversal indicator.
'by' is a charade indicator (letters next to each other).
'family member' becomes 'ma' (ma can informally mean someone's mother).
'breaking into' means one lot of letters goes inside another.
'song' becomes 'aria' (aria is a kind of song).
'it' backwards is 'ti'.
'ma' placed inside 'aria' is 'amaria'.
'ti'+'amaria'='TIA MARIA'
(Other definitions for tia maria that I've seen before include "drink is served?" , "Coffee-flavoured trademarked liqueur" , "Rum-based coffee liqueur" , "Coffee-flavour liqueur" , "After-dinner liqueur" .)