Philosopher Ayer cleaned out horrid toilets (9)
I believe the answer is:
aristotle
'philosopher' is the definition.
(Aristotle is an example)
'ayer cleaned out horrid toilets' is the wordplay.
'cleaned out' suggests removing the centre.
'horrid' indicates an anagram.
'ayer' with its centre taken out is 'ar'.
'toilets' with letters rearranged gives 'istotle'.
'ar'+'istotle'='ARISTOTLE'
(Other definitions for aristotle that I've seen before include "Thinking Greek" , "Ancient Athenian philosopher, pupil of Plato" , "Totaliser for the great Greek philosopher of old" , "noted thinker" , "Greek philosopher (Poetics, Politics)" .)