Your local health department usually specifies the number of drywells, size of drain field or septic tank, and maintains a large file on updated blueprint of septic systems. All new systems are inspected before being covered up and the blueprint should show you the exact layout with measurements. If you still have trouble locating the Dbox, contact your local Roto-Rooter franchise by dialing 1-800-GET-ROTO as their reputation for problem solving is awesome. P.S. The size of your family could have a major impact on the performance of your septic system. If your system requires pumping more than two times in a year, you could have one of the following: root blockage in your drain field, broken or collapsed pipe in drain field (usu. when driven over by heavy vehicle), poor drainage (usu. high water table, clay, or not enough stone), or a failed system.