Causing toilet to change sign (13)
I believe the answer is:
gesticulation
'sign' is the definition.
(thesaurus)
'causing toilet to change' is the wordplay.
'to change' is an anagram indicator.
'causing'+'toilet'='causingtoilet'
'causingtoilet' is an anagram of 'GESTICULATION'.
(Other definitions for gesticulation that I've seen before include "Hand-waving" , "Hand signalling" , "The adding of emphasis by moving arms or hands" , "Hand signal?" .)