ACO backflow preventer provide safe protection against water in cellars. They prevent wastewater from flowing back into the house when the public sewer system is overloaded by heavy rain or blockage occurs. This can lead to a very annoying and costly situation. Who operates a washing machine or shower in the cellar can take advantage of an ACO backflow flap for faeces-free water (grey water) for security. ACO automatic backflow systems for water containing faeces (black water) are utilised for toilets below the top edge of the road outside. These flaps close automatically in the event of a backflow.