Backside clean on reflection? It's what sycophants do (6,2)

I believe the answer is:

butter up

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'it's what sycophants do' is the definition.
I can't judge whether this definition defines the answer.

'backside clean on reflection?' is the wordplay.
'backside' becomes 'butt' (synonyms).
'clean' becomes 'pure' (similar in meaning).
'on reflection?' is a reversal indicator (I've seen 'on reflection' mean this).
'pure' in reverse letter order is 'erup'.
'butt'+'erup'='BUTTER UP'

Can you help me to learn more?

(Other definitions for butter up that I've seen before include "Flatter using dairy product? (6, 2)" , "Flatter in order to get something" , "Soft-soap" , "Flatter for a purpose" , "Flatter to obtain favour" .)

I've seen this clue in The Guardian.

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