Graduate managed to drink last drop of rum - he's often seen in the pub (6)
I believe the answer is:
barman
'he's often seen in the pub' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'graduate managed to drink last drop of rum' is the wordplay.
'graduate' becomes 'BA' (someone with a Bachelor of Arts degree).
'managed' becomes 'ran' (both can mean organised or was in charge of).
'to drink' means one lot of letters goes inside another.
'last drop of' indicates one should take the final letters.
The final letter of 'rum' is 'm'.
'ran' placed around 'm' is 'rman'.
'ba'+'rman'='BARMAN'
Can you help me to learn more?
(Other definitions for barman that I've seen before include "Male who serves in a pub" , "He serves drinks" , "he might be responsible for you getting shot" , "Bloke at counter" , "In pub he might pull" .)