Daily injecting sulphur that may remove impurities (8)
I believe the answer is:
cleanser
'may remove impurities' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'daily injecting sulphur' is the wordplay.
'daily' becomes 'cleaner' (dated term for a woman cleaner).
'injecting' is an insertion indicator.
'sulphur' becomes 'S' (synonyms).
'cleaner' enclosing 's' is 'CLEANSER'.
'that' is the link.
Can you help me to learn more?
(Other definitions for cleanser that I've seen before include "Facial care product" , "Lotion removing grime" , "Preparation to remove dirt" , "Eg, detergent" , "this can remove dirty marks" .)