To install underground drainpipe, lay out the trench, dig it, lay the pipe, and then backfill the trench. You need 4-inch Schedule 40 PVC pipe, flexible drainpipe, PVC primer, PVC cement and a variety of PVC fittings.
- Mark the location of the trench
Place a wood stake at 8-foot intervals, and connect the stakes with string. Mark a chalk line along the string, and then remove the stakes and the string.
- Dig the trench
With a trench shovel or a trenching machine, dig a trench that is at least 6 inches wide and 10 inches deep. To prevent freezing in colder climates, bury the pipe below the frost line. Increase the depth 1 to 2 inches for each section of pipe so that the pipe slopes downward to drain the water.
- Prepare the drainpipes
Position the drainpipes and fittings along the side of the trench.
- Install the pipes
At the top of the trench, measure and cut a section of PVC drainpipe to fit the height of the trench between the drain and a 90-degree elbow. To the connecting surfaces, apply PVC primer and then the PVC cement. Immediately connect the pipe and the fitting. Twist the pipe slightly, and hold it for several seconds while the glue cures. Continue adding sections of pipe and applying the PVC primer and cement until you finish connecting all of the pipes.
- Complete the installation
At the end of the trench, dig a hole about 16 inches deep and 36 inches in diameter. Fill it with 4 inches of gravel. With a hoe or shovel, backfill the trench with dirt.