FRENCH DRAIN MAN on Instagram: "Most People Make These 2 Mistakes When Building a French Drain 1. One of the biggest mistakes when it comes to building a good drain system is people take the excavated dirt, they'll put the pipe in the ground and then they'll put the dirt back on top of the pipe. That's the worst thing you can do. If the soil was any good and it was permeable, we wouldn't be here to begin with. So when you take that non-permeable soil and you excavate it out, you want to haul it