Aaargh, please help! I was advised to put some caustic soda through my sink and bath plug holes as they were slow to drain, which I did today, but when I came to flush it out the bath is fine but the bathroom sink wouldn't clear and instead back-filled to about 2 inches with toilet waste, which is still sitting in there. Sink, bath and WC are all in one room on the first floor of a house with main drainage (no tank).

How can I rectify this gross situation, and also is it likely to be doing any harm to the pipes behind the sink tiling?

Thank you for your help.

Call a plumber and have him snake out the line. Get quotes. It should run between 125 up to 600.