Quantity of liquid served by graduate liable to err (8)
I believe the answer is:
basinful
'quantity of liquid' is the definition.
(amount of liquid held by a basin)
'by graduate liable to err' is the wordplay.
'by' means one lot of letters go next to another.
'graduate' becomes 'BA' (someone with a Bachelor of Arts degree).
'liable to err' becomes 'sinful' (likely to err or sin).
'ba' next to 'sinful' is 'BASINFUL'.
'served' is the link.
(Other definitions for basinful that I've seen before include "Quantity of water" , "More than enough" , "Capacity of a large bowl" .)