To make revelation arrive spotless (4,5)
I believe the answer is:
come clean
'to make revelation' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'arrive spotless' is the wordplay.
'arrive' becomes 'come' (synonyms).
'spotless' becomes 'clean' (similar in meaning).
'come'+'clean'='COME CLEAN'
Can you help me to learn more?
(Other definitions for come clean that I've seen before include "how you hope your home delivery laundry will arrive" , "Reveal dirty secrets" , "how you like your laundry to arrive?" , "Informally, confess fully - arrive washed?" , "Admit" .)