Aftermath of second cleanse (8)
I believe the answer is:
backwash
'aftermath' is the definition.
(synonyms)
'second cleanse' is the wordplay.
'second' becomes 'back' (to second a motion is to back it).
'cleanse' becomes 'wash' (washing is a kind of cleansing).
'back'+'wash'='BACKWASH'
'of' is the link.
(Other definitions for backwash that I've seen before include "Wake" , "Unpleasant after-effects" .)