Septic problem checker
Ranks the likely causes from what you're seeing, and separates the cheap problems from a drain field that has really failed.
The short answer
A full tank, a clogged line from the house, a blocked filter, a failed pump and a failing drain field can all back up the same house. The clues that separate them are where the evidence is — inside, at the tank, or over the field — whether pumping helped, and whether it started with the weather. Tick the symptoms below; nothing you enter leaves your browser.
Tick a symptom to see what usually causes it, ranked — with the cheap causes separated from a drain field that has really failed.
Single symptoms and their most likely cause
What the checker ranks first for each symptom on its own. Combining symptoms changes the answer — two or three together are far more telling than one.
| Symptom | Most likely cause | Where the fault sits |
|---|---|---|
| Only one drain is slow | A clog in one fixture's drain | House plumbing |
| Several drains are slow at once | A clog in the line from the house to the tank | Pipe from the house to the tank |
| Water backs up at the lowest drain | A clog in the line from the house to the tank | Pipe from the house to the tank |
| Toilets or drains gurgle | A dry trap, failed wax ring or blocked vent | House plumbing |
| Sewage smell inside the house | A dry trap, failed wax ring or blocked vent | House plumbing |
| Smell outside near the tank | The tank is overdue for pumping | The tank |
| Smell over the drain field | The drain field is failing | The drain field |
| Soggy ground or standing water over the field | The drain field is failing | The drain field |
| Strips of greener grass over the field | The drain field is failing | The drain field |
| The septic alarm is going off | A failed effluent pump or float switch | Pump, floats or aerobic unit |
| It started after heavy rain or snowmelt | Rain or a high water table has saturated the field | Too much water |
| It happens after laundry or heavy water use | Too much water at once | Too much water |
| The tank hasn't been pumped in 3+ years | The tank is overdue for pumping | The tank |
| It was pumped recently and it's still happening | A clog in the line from the house to the tank | Pipe from the house to the tank |
| Sewage or water is surfacing at the tank | The drain field is failing | The drain field |
| An aerobic unit has gone quiet or smells | An aerobic unit's air pump has failed | Pump, floats or aerobic unit |
How the checker ranks causes
Each cause is scored by how strongly it explains each symptom, and the scores are combined across everything you tick. The weights are deliberately conservative about the expensive answer: a full tank, a blocked filter or a clogged line outranks a failed drain field unless the evidence is out over the field — wet ground, a smell there, or a tank that refills right after pumping.
It also watches for combinations that change what you should do first. Surfacing sewage raises a health warning. An alarm is treated as a pump problem with time to act. Problems that started with heavy rain come with a warning not to have the tank pumped while the ground is saturated, since an empty tank can float.
Which order to check things in
- Is it one drain or all of them? One drain is a plumbing clog, not the septic system.
- When was the tank last pumped? Over three years, or unknown, pump it first.
- Did pumping fix it? If not, the line from the house or the field is the problem.
- Is the ground over the field wet or smelly in dry weather? That's the field.
- Is there an alarm? That's the pump chamber — check the breaker, cut water use, call a septic company.
Frequently asked questions
- How do I know if my septic system is failing?
- Several drains slow at once, backups return soon after pumping, and the ground over the drain field is wet or smells in dry weather. A single symptom on its own is usually something cheaper.
- Why is my septic tank pumped but still backing up?
- The tank wasn't the cause. Either the pipe from the house to the tank is clogged, the outlet filter or baffle is blocked, or the drain field isn't taking water.
- Who should I call for a septic problem?
- A septic pumping or service company for backups, alarms and full tanks; a plumber for a clog in the house plumbing or the line to the tank; an independent inspector before paying for a new drain field.