Char holding top of strong detergent (8)
I believe the answer is:
cleanser
'detergent' is the definition.
(cleansing liquid)
'char holding top of strong' is the wordplay.
'char' becomes 'cleaner' (old-fashioned term for a cleaner).
'holding' means one lot of letters goes inside another.
'top of' indicates taking the first letters.
The initial letter of 'strong' is 's'.
'cleaner' enclosing 's' is 'CLEANSER'.
(Other definitions for cleanser that I've seen before include "Eg, detergent" , "Cleaning cream or lotion" , "Purgative" , "One wanting to get pure" , "Decaying" .)