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 am not sure about the 'in the lab' bit.
'rotters breaking glass' is the wordplay.
'rotters' anagrams to 'RETORTS'.
However, I'm not sure how the anagram 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" .)