Turn off the water at the stop tap.
Syphon off the water from the toilet cistern and soak up the remaining water with a cloth.
Unclip the hook (which connects to the flush handle,)from the diaphram plunger .
Disconnect the two bolts underneath the cistern, ( where the waste pipe connects through the cistern to the syphon)
Remove the whole syphon system, and replace with new. Cost about £9
Good luck
Frank the bodger, August 2008