Rotters breaking glass vessels in the lab (7)
I believe the answer is:
retorts
'vessels in the lab' is the definition.
'retorts' can be an answer for 'vessels' (retort is a kind of vessel). I'm unsure of the 'in the lab' bit.
'rotters breaking glass' is the wordplay.
'rotters' can be anagrammed to 'RETORTS'.
However, I'm unsure how this is indicated.
Can you help me to learn more?
(Other definitions for retorts that I've seen before include "Sharp replies or rejoinders" , "Makes witty or angry reply" , "Counters" , "laboratory equipment" .)