Reckons to drink tot first (4,2)
I believe the answer is:
adds up
'reckons' is the definition.
(reckon can mean to add up)
'drink tot first' is the wordplay.
'drink' becomes 'sup' (to sup is to drink).
'tot' becomes 'add' (synonyms).
'first' says to put letters next to each other.
'sup' put after 'add' is 'ADDS UP'.
'to' is the link.
(Other definitions for adds up that I've seen before include "Totals" , "Tots" , "Reckons" , "Sums - makes sense" , "Puts two and two together" .)