Bowl over toilet? Not quite fun (6)
I believe the answer is:
boggle
'bowl over' is the definition.
(synonyms)
'toilet? not quite fun' is the wordplay.
'toilet?' becomes 'bog' (informal term for toilet).
'not quite' means to remove the last letter (most but not all of the word).
'fun' becomes 'glee' (I've seen this before).
'glee' with its final letter taken off is 'gle'.
'bog'+'gle'='BOGGLE'
(Other definitions for boggle that I've seen before include "Fluster and flabbergast" , "Be startled or baffled (colloq.)" , "Baffle or fluster" , "Be surprised or baffled" , "Overcome with amazement" .)