The blockage may be in the big pipe at the back of the WC pan and around the bend - it may be in the foul water pipe outside and it may be in the outlet pipe to the main sewer.
If you have an outside inspection pit then lift the lid and look inside - it will give you an indication of where the blockage may be.
Peccavi
July 2010
you have a blockage,stopping the water from syphoning away hence filling up
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