I am planning to lay some corrugated flexible drain tile with the sock in the back yard to help with a wet back yard. There is currently some drain tile that I assume comes from the exterior of the foundation (walk out basement) that needs to be extended to the storm sewer in the back corner of our lot. I also plan to add drain tile from the gutter down spouts to move the water to the storm sewer too. The distance from the house to the storm sewer is about 40 feet and drops about a ¼ per foot. The drain tile will only be under 2 -3 of soil. I have been thinking about running two separate runs of drain tile to keep the foundation and gutter down spout separate. My thought is that if there is a lot of volume running from the down spout there would be a risk that the water would back up toward the foundation. Are two runs a good plan or is it over kill. Will corrugated flexible drain tile be strong enough? What else should I be thinking about?