Is present there, I say, after a non-drinker finishes (7)
I believe the answer is:
attends
'is present' is the definition.
(to attend something is to be present at it)
'after a non-drinker finishes' is the wordplay.
'after' means one lot of letters go next to another.
'non drinker' becomes 'tt' (abbreviation for teetotaller).
'finishes' becomes 'ends' ('end' can be a synonym of 'finish').
'a' next to 'tt' is 'att'.
'att'+'ends'='ATTENDS'
'there i say' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for attends that I've seen before include "Waits on or is present" , "ministers" , "Pays attention" , "Heeds" , "to listen carefully" .)