apparatus for forming and installing underground drainpipe in subterranean passages . the pipe is formed from a web of porous or non - porous sheet plastic which is drawn from a dispensing roll through curling and shaping devices protected by a transparent shield to provide a tube , these devices being mounted on a frame positionable in a trench or other depression in the soil . the end of the tube is attached to a mole at the end of a power driven blade , with the mole forming an underground passage for the following tube . tensioning and positioning rollers are carried on the frame to feed the web to the tube forming devices at a predetermined angle and tension . a pressor roller and its support bracket interengage complimentary tongues and slots formed along the edges of the web for holding the web in its tubular form .