Unfortunately people sometimes connect into the wrong sewer - either by accident or deliberately. Often the householder will install an automatic washing machine or dishwasher in a kitchen or utility room and use the nearest drain for the out pipe. This may be the drain receiving the rain pipe from the roof, which is connected to a surface water sewer. Sometimes bathrooms and whole houses are wrongly connected.
If foul sewage is put into a surface water sewer it will result in the pollution of the river or stream into which it discharges. This is illegal and the owner of the wrong connection could face prosecution. If you are in doubt, please contact us.