Final, crushing defeat of the modern toilet? (8)
I believe the answer is:
waterloo
'final crushing defeat' is the definition.
(I've seen this before)
'modern toilet?' is the wordplay.
'modern' becomes 'water' (I can't justify this - if you can you should give a lot more credence to this answer).
'toilet?' becomes 'loo' (loo can informally mean a toilet).
'water'+'loo'='WATERLOO'
'of the' acts as a link.
Can you help me to learn more?
(Other definitions for waterloo that I've seen before include "Historic battle" , "Eighteen hundred and fifteen battle" , "Belgian battle site" , "Seminal European battle of 1815" , "railway terminal" .)