A battle fixing toilet after flood (8)
I believe the answer is:
waterloo
'a battle' is the definition.
(1815 battle)
'toilet after flood' is the wordplay.
'toilet' becomes 'loo' (loo can informally mean a toilet).
'after' is a charade indicator (letters next to each other).
'flood' becomes 'water'.
'loo' after 'water' is 'WATERLOO'.
'fixing' acts as a link.
(Other definitions for waterloo that I've seen before include "Napoleonic end" , "battle in Belgium" , "Battle - station" , "Napoleon's final battle" , "Belgian battle site" .)