A drink knocked up in Tuscan city (4)
I believe the answer is:
pisa
'tuscan city' is the definition.
(I've seen this before)
'a drink knocked up' is the wordplay.
'drink' becomes 'sip' (sipping is a kind of drinking**).
'knocked up' says the letters should be written backwards.
'a'+'sip'='asip'
'asip' written backwards gives 'PISA'.
'in' is the link.
(Other definitions for pisa that I've seen before include "Italian city with famous tower" , "There's a marked inclination here" , "Site of the famous leaning tower" , "Italian city with leaning tower" , "City with listed building" .)