Slowly filter into bar returning for a drinking session (5-2)
I believe the answer is:
booze-up
'drinking session' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for booze-up that I've seen before include "Bout of serious drinking" , "Drinking spree" , "Heavy drinking session" .)