Promotion gets date to drink tots (4,2)
I believe the answer is:
adds up
'tots' is the definition.
('add up' can be a synonym of 'tot')
'promotion gets date to drink' is the wordplay.
'promotion' becomes 'ad' (short for advert).
'gets' is a charade indicator (letters next to each other).
'date' becomes 'd' (abbreviation e.g. dob - date of birth).
'to drink' becomes 'sup' (to sup is to drink).
'ad'+'d'+'sup'='ADDS UP'
(Other definitions for adds up that I've seen before include "Stands to reason" , "Puts two and two together" , "Sums - makes sense" , "Reckons" , "Totals" .)