Public sewers are designed for average rainfall events only, for purely economic reasons, and not for extreme events such as heavy rainfall. Heavy precipitation overloads the sewers and the back-flowing water rises in the sewer manholes up to the back-flow level. To the same extent, the back-flowing wastewater pushes back into the plot drainage system of the surrounding houses.
Apart from the installation site and delivery head, the quality of the wastewater is another important aspect for choosing the right lifting plant. Wastewater from washing machines or washbasins, so-called grey water (non-faecal wastewater), does not contain any bulky solids. It can therefore be transported more easily than black water (faecal wastewater), which is soiled with human faeces. Lifting plants for faecal wastewater are therefore designed to easily transport solids without blocking.