Use the tape measure and dry marker to identify on the pipe were the center of the bend is to be placed. A general rule of thumb for bending the pipe is to place another mark 6 to 10 inches on both sides of the center mark of the bend. This will be the "heat zone" of the pipe--the area to apply heat from the heat gun.
Set the radius forms next to the pipe that you are going heat. The closer the can or bucket is to the pipe, the easier it will be to form the pipe bend. The can or bucket should be set on end with the open side facing upwards.
Lay the marked piece of pipe on the two scrap pieces of 2-by-4s. The end heat zone marks should be inside the 2-by-4s with the pipe supported off of the ground.
Plug in the heat gun and turn it on. Hold the heat gun approximately 2 to 3 inches from the pipe to prevent scorching of the plastic surface.
Move the gun slowly over the length of the marked heat zone. With every pass to each black mark, turn the pipe in a clockwise direction about a quarter of a turn.
Heat the pipe until the plastic begins to sag in-between the two scrap 2-by-4 supports.
Shut the heat gun off and lay it to the side away from you so you do not burn yourself.
Grasp the sagging pipe on both side of the heat zone marks and gently lay it over the radius form. Gently form the pipe over the round surface and roll it in a clockwise direction to keep the pipes shape. At the same time, pull the pipe around the form to shape the bend you desire.
Lay the pipe to the ground once the shape has been formed and gently wipe the warm pipe with the wet rag. The wet rag will aid in cooling the pipe and set the bend to re-harden the plastic.