Measure the outside diameter of the HDPE pipe with a tape measure. Select a plumbing anchor baseplate and mounting collar having the same diameter as the pipe.
Cut a hole, 1/8-inch larger than the outside diameter of the pipe, through the wall, floor or ceiling with a drill and hole-saw. Place the anchor baseplate over the hole, and secure the baseplate with wood screws and a screwdriver. Run the pipe through the hole in the baseplate.
Place the top and bottom halves of the anchor plate collar around the pipe. Connect the collar halves with the supplied bolts, and twist the bolts in place with your fingers; leave the collar loose enough to slide along the surface of the pipe.
Push the collar up against the anchor baseplate -- and tighten the collar to the baseplate with a Phillips screwdriver and the supplied screws.
Tighten the collar bolts, with a wrench, until the collar is firmly engaged against the pipe.