My house was built in the early 50s. It has a well and septic. I believe the basement floor is much lower than the bottom of the septic tank. There are 4 floor drains in the basement, one of which the washer drains into, one had a toilet which I removed, and two others are larger and have grated covers. Where do these drains lead to? They have never backed up. The waste drain from the home exits the basement wall horizontally, 4 feet above the floor and leads to the septic tank about 15 feet from the foundation. There is no drain tile around the foundation. Any ideas where the drains go?