A French drain is a trench filled up with small rocks, gravel or a perforated pipe that allows for surface water to be redirected away from one area to another area. In the case of the perforated pipe scenario, the French Drain can have the top or bottom of the pipe perforated. In both cases it is to quickly vent seeping water that seeps down through the upper rock or gravel layer. French drains can be used behind retaining walls to relieve build up ground water pressure, but also to move and redistribute the water such as a septic drain field at the end of a typical septic tank. Soil tests are offered to best determine drainage strategy. Other words for French drains are: weeping tile, blind drain, rubble drain, rock drain, drain tile, perimeter drain, land drain, French ditch, sub-surface drain, sub-soil drain or agricultural drain.