Wait on non-drinker, being after a tip (6)
I believe the answer is:
attend
'wait on' is the definition.
'non-drinker being after a tip' is the wordplay.
'non drinker' becomes 'tt' (Teetotaller abbreviation).
'being after' says to put letters next to each other.
'tip' becomes 'end'.
'tt' put after 'a' is 'att'.
'att'+'end'='ATTEND'
(Other definitions for attend that I've seen before include "Take part in" , "Listen closely" , "Be present or appear at" , "Wait upon or be present" , "Concentrate carefully" .)