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' says to hollow out the word (remove centre letters).
'horrid' indicates anagramming the letters.
'ayer' with its middle removed is 'ar'.
'toilets' is an anagram of '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)" .)