That one about the chap who's always buying drinks? (8,4)
I believe the answer is:
standing joke
'that one about' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'chap who's always buying drinks?' is the wordplay.
I cannot quite understand how this works, but
'chap' could be 'tan' and 'tan' is present in the answer.
This explanation may well be incorrect...
'the' acts as a link.
Can you help me to learn more?
(Other definitions for standing joke that I've seen before include "Constant source of amusement" , "Regular source of amusement or ridicule" , "Regular cause of amusement" , "laugh" .)