City Drain In Backyard . The easement is pretty large and i was told that i. A typical plumbing drain system consists of a network of pipes. Yard Drainage Systems Oklahoma City French Drains in Edmond & OKC from billscustomconcrete.com So the backyard slopes down towards the basin and apparently, the water flows from surrounding neighbors' homes to this basin all season long so there is a possibility of the area being flooded (worst case) or have a pool of water making the. Of slope per foot of tubing (1/2 in. It is probably about 15 feet away from the foundation.