A French drain is a pipe with holes throughout its length that is used to assist yard drainage. If your yard is low-lying and water tends to stand, causing soggy or muddy ground, a French drain may help encourage that water to continue moving through instead of collecting. Cleaning a French drain on a regular basis is important in order to not have the holes in the pipe fill with dirt, preventing water flow in and out. When the drain becomes clogged, water will back up and not drain out of your yard.
Find one end of the French drain. You should be able to find a hole in the ground where one end of the French drain begins. If you are not sure where the start of the drain is, it is best to look near the high point on your yard is, as the drain helps water run downhill.
Run water down the drain. Using your garden hose, send water down the drain. If the water backs up instead of running through, you can be sure that you do have a clog.
Try unclogging the drain with a pressure washer. This will send water at a high pressure down the drain. Stand to the side when doing this as the water may come back out at you when it reaches the clog. Try to aim the pressure washer water toward the bottom of the drain to dislodge the clog. Move the spray around, cleaning all sides of the pipe.
Use a sewer snake to clean out stubborn clogs. If the pressure washer does not clean out the clog, the water will continue to back up out of the drain. A sewer snake is a long piece of piping that you can stick down the drain until it reaches the clog, where it will stop moving. Push gently on the clog to attempt to free it up. When it feels looser or breaks free, use the pressure washer again to ensure that the entire clog breaks up and dissipates down the drain. Continue using the sewer snake and pressure washer until the water flows freely down the drain.