French Drains
4. Pour the Gravel. Pour 3 inches of gravel in the trench and make sure that it is compact. This initial layer of gravel will act as bedding for the drainpipe. This is just the first layer of gravel. More will be poured at the top of the drainpipe. Some people don't follow this method but the drainpipe should be sandwiched between the gravel. 5.