Ingrown roots in city owned sewage pipes is a unsolved problem since endless years. T The rubber seals are fulfilling the according proof standards (for ex. DIN 4060/DIN EN 681) regarding root proofness, but apparently these normative requirements are not enough. The IKT Gelsenkirchen already noticed this problem as well as other operators of sewage facilities.
More informations: ikt-short report
Infomap: