When flushing the toilet, the waste overflows up and into the adjoining waste gulley from the bath/ basin. The stench pipe and bath/basin pipes are located approx. 3 feet apart. I cannot locate an inspection chamber, and do not know where the wastes go to, as I have inserted an outside hose to the gulley, checked with adjoining neighbours and no water flows through their drains. The water must be going somewhere, because it does not overflow when I insert the hose into the gulley and blast in water at full pressure. I am baffled as to why the sewerage overflows after each flushing. Please help.