US Patent 7134808 Drain sealing

Plastic liner sections define a drainage channel when placed end to end. Each end has a stiff, double walled flange at each side of the end adapted to butt up to a similar flange at the adjacent end of the next sections. The double walled construction of the flanges stiffens the ends significantly reducing the risk of deformation by the hydrostatic forces produced by wet concrete during installation. A groove is formed inwardly of the flanges on a female end of the liner section and receives a sealing ring, which is held in place by a lip formed on a male end.