The flush on the toilet is a push in button rather than push down button. It often sticks leaving water pouring into the toilet and draining the tank. How do I access it? It can't be from the top as I have a granite fitted top and the button is lower down behind the toilet.
The push button is probably ,or should be fitted in a removeable panel.If there is gap all round the panel
where the button is fitted just pull it and and you should have access.
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Try fixfault.com to fix toilets.