Extend a gutter downspout by laying out and digging a trench for the extension, connecting the downspout to a PVC adapter, installing the pipe extensions and burying the pipe. Extending a downspout requires several different lengths and shapes of schedule 40 6-inch diameter PVC tubing, PVC fittings, a downspout adapter, PVC priming compound and PVC cement. Tools required for this job include a shovel for digging the trench and a small hacksaw for cutting tubing.
Before you dig the trench for the tubing, lay it out using stakes and string, and then spray-paint the final shape of the trench onto the ground. When digging the trench, start out with a hole that is 6 inches wide by at least 10 inches deep. As you get further from the downspout, gradually pitch the trench by about 1 or 2 inches for each few feet of pipe to ensure that water flows easily through the system. When digging the trench, place all of the dirt in several cardboard boxes along the side, as this makes filling the trench back in much easier and reduces the aesthetic damage to your landscape.
Dry-fit all of the pipes and fittings before gluing the system together. To connect the pipes and fittings, swab each surface with a thin coat of primer, and then immediately apply the cement. Hold the two pieces together firmly for a few seconds to allow the cement to solidify. After connecting all of the pieces, attach the downspout to the adapter and fill the trench back in.