Beatnik recalled poo lining old river (4-3)
I believe the answer is:
drop-out
'beatnik recalled poo lining old river' is the definition.
I can't judge whether this defines the answer.
'beatnik recalled poo' is the wordplay.
I cannot really understand how this works, but
an anagram of 'poo' is 'opo' which is within the answer.
The remaining letters 'drut' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for drop-out that I've seen before include "Unsuccessful student" , "start at Rugby" .)