Gutter downspouts that drain freely into a splash tray beside your house can cause serious water damage, including flooding your crawl space or basement. To avoid these problems, bury your gutter downspout and direct the storm water flow away from your house. Before burying your gutter downspout, check with your local zoning or building authority about rules or guidelines governing storm water drainage. Some municipalities require you to drain the water into an underground storm sewer system or otherwise direct the water in a specific fashion.
Run a 12-inch length of the downspout pipe at a 90-degree angle toward the ground, extending it outward from the house. Keep this section of the downspout above ground to prevent the pipe from becoming crushed by the settling dirt around the house's foundation.
Inspect the slope of your property and plan the route in which you want to lay the downspout pipe. The gutter downspout drain line needs to slope away from the house and downward at a rate of 1/8-inch descent for every 1 foot of pipe.
Dig a trench along the desired route of the drain pipe. Make the trench the same width as the downspout pipe and about 12 inches deep. If your yard is flat or doesn't naturally have the desired slope, dig the trench deeper as it extends away from the house to create the slope.
Lay the downspout drain pipe in the trench. Backfill the dirt and tamp it down gently. Ensure that the far end of the drain line is free of obstructions and drains freely.
Inspect the ground above the buried downspout after the first two or three substantial rainfalls. Check that water is not pooling around the drain line, indicating a leak in the downspout piping.