Q. Our household plumbing is having drainage problems, and I’m not sure why. How do you determine if the problem is the septic tank and not the drainage lines?
A. You must open the tank. Septic tanks are partitioned. The inlet side is intended to capture and hold most of the waste during the decomposition stage—it floats, decomposes, and then the remaining solids are left to settle to the bottom. These solids must periodically be cleaned out (recommended by septic tank guys every 4 to 5 years). The remaining liquid soup on the inlet side migrates through an opening in the partition at mid-height of the tank into the outlet side. The mid-height opening is supposed to prevent the floating and bottom-dwelling solids from migrating to the outlet side. If the tank has filled above the outlet to the field lines, there is probably a field line blockage. Usually this will be accompanied by seepage to ground surface between the tank outlet and the blockage, resulting in stinky wet spots in the yard. Seldom is the tank the source of the problem unless it has not been cleaned in a long time. Theoretically, excessive tank sludge could be hindering the overflow into the outlet side and into the field lines. If the field line outlet is open, the inlet side of the tank may be “oversludged,” and a cleanout may solve the problem (and cost much less than a field line job). All the above assumes there is no blockage between the house and the tank.