Queue endlessly to get disinfectant (8)
I believe the answer is:
formalin
'disinfectant' is the definition.
(I've seen this before)
'queue endlessly' is the wordplay.
'queue' becomes 'form a line'.
'endlessly' means to remove the last letter.
'formaline' with its last letter removed is 'FORMALIN'.
'to get' acts as a link.
(Other definitions for formalin that I've seen before include "Preservative" , "embalming fluid" , "Disinfectant" , "preserving solution" , "antiseptic" .)