Endlessly drink something sticky, sugary fluid (6)
I believe the answer is:
nectar
'sugary fluid' is the definition.
(I've seen this before)
'endlessly drink something sticky' is the wordplay.
'endlessly' means to remove the last letter.
'drink' becomes 'neck' (to neck a drink is to drink it quickly).
'something sticky' becomes 'tar'.
'neck' with its final letter taken off is 'nec'.
'nec'+'tar'='NECTAR'
(Other definitions for nectar that I've seen before include "Sugary stuff in plants to attract insects" , "Sweet liquid of the gods" , "Sweet floral secretion" , "very nice drink" , "Trance (anag)" .)