Revolting metro bins might be source of rotten smell (9)
I believe the answer is:
brimstone
'source of rotten smell' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'revolting metro bins' is the wordplay.
'revolting' indicates anagramming the letters.
'metro'+'bins'='metrobins'
'metrobins' with letters rearranged gives 'BRIMSTONE'.
'might be' is the link.
Can you help me to learn more?
(Other definitions for brimstone that I've seen before include "Old name for sulphur" , "It robs men (anag) - old word for sulphur" , "Insect" , "Biblical sulphur that rained with fire on evil cities" , "Sulphur; butterfly" .)