We thought our newly purchased toilet would save water because of the dual-flush mechanism. (Sometimes a smaller flush is all that's needed and using it saves water.) Having been warned about the overflow problem, we looked inside the cistern and could see the mark to which the water should fill. Initially it filled to that mark but, when we looked later, it had filled right up to the top of the overflow pipe, as can be seen in the left hand picture. The overflow pipe takes any excess water into the pan, rather than to outside, as used to happen. This means a toilet doesn't need to be near an outside wall but it is much less obvious when the water is overflowing. The water was flowing very slowly down the pipe but was not really noticeable inside the pan. We have now had repairs done to correct this fault.