Sewage Is Coming Back Into the House. What Now?

Jim Anderson
Jim Anderson

Recently I had a reader ask what he should inspect when there is a tank backup. I took this question to mean what should be looked for when the system is backing up into the house, rather than simply a tank problem. Based on discussions over the years, this question is probably similar to requests that you come out to look at and fix a backed up septic system. The following are some of my thoughts on what to troubleshoot to determine the cause of the backup, which leads to the solution of the problem.

I would start by asking a couple more questions before heading to the backyard to look at the tank. First, I want to find out if there is a sump with a pump in the basement or lower level of the home. If so, the problem could be with the sewage pump and sump and have nothing to do with the rest of the system.

If the answer is that everything flows out of the house sewer by gravity, then opening the tank is probably the next step unless there is a readily available clean-out for the sewer line that can be evaluated for a blockage in the line with either a snake or camera. Where I live, if there is any type of bow in the sewer pipe, it is subject to freezing during extreme cold weather; so the sewage does not make it to the tank! There was a lot of this in my area where we reach ambient air temperatures of 31 degrees F below zero. That’s not wind chill, but the actual temperature.


Next, I am going to inspect tank contents and the inlet and outlet baffles. If the tank contents are at the proper level, the inlet should be inspected carefully because a proper level means the blockage is either in the house sewer pipe or at the inlet.

Common conditions to look for:

  • Is there adequate space between the inlet pipe and any cast-in-place baffle for sewage and associated solids to enter the tank? If the pipe was inserted too far during installation, toilet paper and other products that may have been flushed can hang up between the pipe and baffle.
  • Does the sewer pipe come straight in or is cocked at an angle? This would cause solids to hang up in the pipe, eventually blocking the pipe. This is usually caused by tank settling or the pipe not being properly supported.

If the contents are above the invert of the outlet pipe, the tank should be pumped and evaluated. The outlet baffle, effluent screen and the piping leaving the tank should be inspected. If the baffle and effluent screen are in place where they should be, inspecting the effluent screen should determine if this is the problem. The outlet pipe should be inspected for evidence it leaves at an angle or is out of round. If so, the tank has settled or piping was not properly installed and is not allowing effluent to leave the tank.

If water runs into the tank through the outlet, the problem is downstream from the tank. Any pretreatment component or pump tank downstream should be evaluated. In the case of a pump tank, there should be a separate alarm to indicate a problem with the pump. If there is no alarm, the tank should be pumped and the pump evaluated to see if it is operating properly and delivering the correct amount of effluent to the soil treatment part of the system.


Piping to the soil treatment system should be evaluated for any blockages caused by solids, roots or freezing. If the piping is empty — as it should be — the problem lies in the soil treatment unit or soil. This is where access to drop or distribution boxes is very important to allow you to determine how the system is operating. Is effluent reaching all parts of the treatment unit, or is there a distribution problem of some sort? With ready access from the surface to each trench, it is easy to determine if all trenches are being used.

If one trench has effluent and the others none, the system is not operating the way it is supposed to. Not long ago, I had a discussion with a service provider doing an inspection of a system with periodic backups where only one trench out of three was being used. He wanted to approve the system because the problem would not get any worse and the current residents could get along the way it was without finding out why only one-third of the system was used. The system was not operating the way it should and needed to be fixed.

If the soil treatment unit is full and backing effluent to the house, household water use, size of the system and soil characteristics in the soil treatment area must be evaluated. There may be a limiting soil condition, water use may be exceeding system capacity or there were some installation or design mistakes.

Sorting out these issues can be time consuming, and the fix is probably going to be costly to the homeowner. But if you have reached this conclusion after thoroughly inspecting all parts of the system, it will be much easier to have a conversation with the homeowner about the need for a new soil treatment system.


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