Bird raised in hollow is cleaner (9)
I believe the answer is:
detergent
'is cleaner' is the definition.
(chemical that cleans)
'bird raised in hollow' is the wordplay.
'bird' becomes 'egret' (egret is a kind of bird).
'raised' is a reversal indicator (going up in a down clue).
'in' means one lot of letters goes inside another.
'hollow' becomes 'dent' (both can mean an impression or indentation).
'egret' reversed gives 'terge'.
'terge' inserted within 'dent' is 'DETERGENT'.
(Other definitions for detergent that I've seen before include "Cleaning product" , "Soluble cleanser" , "Cleansing substance used for washing clothes" , "cleaner" , "Get tender (anag)" .)