Book is nothing after a couple of pints (6)
I believe the answer is:
quarto
'book' is the definition.
(I know that quarto is a type of book)
'nothing after a couple of pints' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'after' is a charade indicator (letters next to each other).
'a couple of pints' becomes 'quart' (a quart is equal to two pints).
'o' put after 'quart' is 'QUARTO'.
'is' acts as a link.
(Other definitions for quarto that I've seen before include "Book size resulting in folding one sheet four times" , "Twice-folded paper size" , "Ten-by-eight inch paper" , "Book page size" , "Publishing term, four leaves are formed from one sheet" .)