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Quick answer
A septic smell usually comes from sewer gas escaping where it should not, or from a tank, filter or drain field that is not working properly. Where you smell it points to the cause: indoors often means a dry drain trap or vent problem, near the tank means a lid or pump issue, and over the field can mean saturated soil.
A faint whiff after a long vacation is one thing. A steady sewage smell in the yard or the hallway is your system trying to tell you something. The good news is that the location of the odor narrows down the cause quickly, and many causes are simple. A few are not, so it helps to know which is which.
What does a healthy septic system smell like?
A conventional system should have almost no odor around the yard. An aerobic system should smell faintly earthy or musty at most, because the treatment process uses oxygen. A strong rotten-egg or raw sewage smell means gases are escaping that should stay in the pipes and tank, or the treatment is not working as it should.
Why does it smell inside the house?
Odors inside are usually a plumbing problem rather than a tank problem, and they are often the easiest to fix.
- A dry drain trap. Every sink, shower and floor drain has a curved pipe that holds water as a seal. If a guest bathroom or a floor drain has not been used in weeks, the seal evaporates and gas comes up. Run water for a minute to refill it.
- A blocked or damaged plumbing vent. Vent pipes let gas escape through the roof. A bird nest, debris or a cracked pipe can push the smell back into the house.
- A loose toilet seal. If the wax ring has failed, you may smell sewer gas around the base of the toilet.
- A slow drain or partial blockage. Food and soap residue sitting in a drain line can smell on its own.
- A tank that is too full or backing up. Gurgling, slow drains in several fixtures and a smell together suggest the tank, filter or line outside needs attention.
Why does it smell near the tank?
Some odor near the lids is normal when the tank is opened. A constant smell is not.
- A cracked, loose or missing lid or riser cap that lets gas out. See septic tank lid replacement.
- An aerobic system whose air pump has stopped or weakened. Without oxygen the bacteria switch over to a process that produces a sewage smell.
- A clogged effluent filter or a failed discharge pump that is holding water in the tank longer than it should.
- A tank overdue for pumping. Check how often to pump your septic tank if you are not sure when yours was last done.
- Harsh chemicals or a large dose of disinfectant that killed off the bacteria.
Why does it smell over the drain field or spray area?
A smell over the field means untreated or partly treated water is near the surface, or the soil is too wet to absorb it.
- Wet, soggy or unusually green grass above the field or lines.
- Standing water, black soil or a damp patch that does not dry between rains.
- A spray head that is clogged, broken or watering one spot too heavily.
- A field that has been overloaded by water use or by heavy rain. Greater Houston's clay holds water and drains slowly, which makes this common. Read how clay soil affects septic systems.
Which smells are urgent and which can wait?
Call soon if you notice any of these:
- Sewage rising in a tub, shower or floor drain, or backing up into the toilet.
- Wastewater at the surface of the yard, especially near children or pets.
- An alarm that is sounding or flashing along with the odor.
- A strong gas smell indoors that does not clear after you open windows. Leave the area and call for help.
These can usually wait a few days while you do the checks below: a faint smell after being away, a smell in one rarely used bathroom, or a mild odor after a big laundry day.
What can you check yourself?
- Run water in every drain for a minute, including floor drains and guest bathrooms.
- Look at the control panel. If a light or alarm is on, note it. See what the red alarm light means.
- Walk the yard. Look for wet spots, sinking soil or spray heads that look wrong.
- Check that the lids are in place and not cracked.
- Think about the last week: heavy rain, many guests, a lot of laundry, a new cleaning product.
Do not open the tank to look inside. Gas in a septic tank can be dangerous to breathe, and tank openings can be hazardous. Leave that to a professional.
When should you call a septic company?
Call if the smell comes back after you have refilled drains, if it is strong, or if it is paired with slow drains, wet ground or an alarm. We can inspect the tank, filters, pumps and dispersal area, and our septic repair team can fix what we find. If you are not sure whether the system itself is the source, call Brown Aerobic at 832-789-5357 and describe what you smell and where.
Quick questions and answers
- Why does my septic tank smell worse after rain?
Heavy rain saturates the soil and slows how fast the field can absorb water. That can push gas up near the tank and field, and in low-lying yards it can hold water at the surface. If the smell stays after the ground dries, have it checked.
- Is septic smell dangerous?
Sewer gas from a tank can be harmful in enclosed spaces. A faint outdoor odor is mostly a nuisance, but a strong gas smell indoors or sewage at the surface should be treated seriously. Ventilate and call for service.
- Why does my aerobic septic system smell like sewage?
An aerobic system should smell mild. A sewage smell often means the air pump has stopped or the filter is clogged, so the bacteria are not getting oxygen. Check the panel for an alarm and call us.
- Will pumping the tank get rid of the smell?
Sometimes, if the tank was overdue. If the smell comes from a dry trap, a vent, a failed pump or a saturated field, pumping alone will not fix it. A short inspection tells which it is.
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