Crowning achievement - emptied flipping chamberpot (4)
I believe the answer is:
atop
'crowning' is the definition.
(I've seen this in another clue)
'achievement emptied flipping chamberpot' is the wordplay.
'emptied' says to hollow out the word (remove centre letters).
'flipping' shows that the letters should be reversed in order.
'chamberpot' becomes 'po' (old-fashioned informal term for a chamber pot).
'achievement' with its middle taken out is 'at'.
'po' in reverse letter order is 'op'.
'at'+'op'='ATOP'
(Other definitions for atop that I've seen before include "on the head" , "Upon" , "Positioned on" , "Surmounting" , "Covering" .)