One sort guzzling another quiet drink (4,5)
I believe the answer is:
milk shake
'drink' is the definition.
(milk shake is a kind of drink)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for milk shake that I've seen before include "Dairy/fruit drink" , "Cold whisked drink" , "Dairy drink" , "Frothy mixed drink" .)