Sanitise with chlorine each November - extremely simple (7)
I believe the answer is:
cleanse
'sanitise' is the definition.
(I've seen this in another clue)
'chlorine each november extremely simple' is the wordplay.
'chlorine' becomes 'Cl' (Cl is the chemical symbol for chlorine).
'each' becomes 'ea' (abbreviation).
'november' becomes 'N' (phonetic alphabet: alpha, bravo, charlie etc.).
'extremely' says to hollow out the word (remove centre letters) (letters on the extremes of the word are used).
'simple' with its middle taken out is 'se'.
'cl'+'ea'+'n'+'se'='CLEANSE'
'with' is the link.
(Other definitions for cleanse that I've seen before include "Thoroughly remove dirt from" , "Bathe" , "give absolution" , "Disinfect" , "Scrub" .)