Flex-Drain 4"x8' Black Expandable Solid Flex Drain. It expands from 2' to 8' and can be used in most drainage applications. Soil tight fittings are built into the pipe and the pipe holds its shape after it is bent, therefore no other connectors are needed. Simply dig your trench, lay your flex drain pipe and cover it up. It meets the Corrugated Polyethylene Pipe Association's Test for Crush Resistance.