Sightseers here perhaps inclined to knock back a little drink (4)
I believe the answer is:
pisa
'sightseers here perhaps inclined' is the definition.
The answer is a location as well as being a singular noun. This is suggested by the definition.
'knock back a little drink' is the wordplay.
'knock back' says the letters should be written backwards.
'a' becomes 'an'.
'little' means to remove the last letter (the word is not quite complete).
'drink' becomes 'sip' (I've seen this before**).
'an' with its final letter taken off is 'a'.
'a'+'sip'='asip'
'asip' backwards is 'PISA'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for pisa that I've seen before include "much-visited city" , "Place with leaning tower" , "There's a marked inclination here" , "Tuscan city" , "Italian city with leaning tower" .)