A drink? Yes, that's right (3)
I believe the answer is:
jar
'a drink?' is the definition.
(colloquial)
'yes that's right' is the wordplay.
I cannot quite understand how this works, but
'right' could be 'ar' (I've seen this in other clues) and 'ar' is found in the answer.
A single letter 'j' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for jar that I've seen before include "Enduring courage" , "Glass of beer; clash" , "Storage container" , "Grate" , "(Jam) pot" .)