A French Drain is completely different from a Surface Drain. A basic French Drain consists of a Perforated Drain Pipe in the bottom of a trench. A Trench Liner is sometimes used depending on the Drainage System Design and the type of soil. The Drain Pipe should have a neoprene sock around the Perforated Drain Pipe. This is to ensure that the Drain Pipe does not become clogged. A trench is dug that is slightly wider than the French Drain Pipe that is being used. There are several sizes of French Drain Pipe. Three Inch, Four Inch, and Six Inch are the most common sizes of French drain Pipe. The dirt that is taken out to make the trench is hauled away. It is replaced by some type of small stone or gravel depending on what is desired or available. I prefer crushed 1 inch lime stone. It is the most economical option in my area. Pea Gravel or some other type of small stone can work just as well. The lime-stone or gravel is placed in the trench on top of the perforated Drain Pipe and filled all the way to the surface (ground level). In some cases where the French Drain needs to be deep or is being placed in sandy soil, a special trench liner must be placed in the trench before the perforated Drain Pipe or the Gravel are installed. This helps maintain the integrity of the trench over time. It also increases the cost of the French Drain and the amount of time to install it. I install a trench liner in a French Drain about 20% of the time. Most of the time a liner in not needed.