Flask makes a come-back (6)
I believe the answer is:
retort
I believe this is a double definition.
'flask' is the first definition.
(type of flask in chemistry)
'a come-back' is the second definition.
'makes' is the link.
(Other definitions for retort that I've seen before include "Glass vessel used in distilling liquids" , "one used in lab" , "Sharp rejoinder" , "Quick and clever or angry reply" , "Come back" .)