Why Does Your House Smell Like Sewer Gas?

We get a couple of calls every month from homeowners who say their house smells like sewage, and the first thing I tell them is that the smell does not automatically mean the septic system has failed. A lot of odor problems start inside the plumbing. A dry trap, a bad vent, or a failed toilet seal can make a house smell terrible even when the tank and drain field are working normally.

The location of the smell usually gives you the first clue

If the odor is strongest around one sink, shower, or floor drain, I start thinking about the plumbing at that fixture. Every drain has a trap that holds a small amount of water and blocks sewer gas from coming back through the pipe. In a guest bathroom or another area that does not get used much, that water can evaporate and leave the drain open to the plumbing system. That is one of the few sewer-odor problems a homeowner can safely fix in about a minute. Run water into the unused drain and see whether the smell improves.

A toilet can cause the same kind of problem for a different reason. The wax ring underneath it seals the toilet to the drain connection. If that seal fails, sewer gas can escape around the base, and you may notice the odor close to the floor. A toilet that rocks when you push on it or shows moisture around the base deserves a closer look.

Plumbing vents are another common source, especially in new construction. The vent system is supposed to carry sewer gas out through the roof while keeping the drainage system working properly. If the vent was installed incorrectly, left incomplete, blocked, or disconnected, the odor can end up inside the house instead. In the calls we get from newer homes, bad venting is one of the first things I think about.

Homes with pump systems can have another unusual source. The electrical conduit running between the septic equipment and the control panel can give gas a path toward the house if it is not sealed correctly. That is not something I would recommend a homeowner start taking apart because now you are dealing with both septic gas and electrical components.

Septic problems usually bring other symptoms with the smell

Odor becomes more suspicious for a septic problem when it is stronger outside around the tank or drain field. I pay even more attention when the smell comes with slow drains, gurgling, wet ground, or a backup inside the house.

Heavy rain can make those symptoms more obvious. A weak or saturated drain field may struggle more when the surrounding soil is already wet. If the odor gets worse after storms and the drain field stays soggy, I want to look at the septic system rather than assume somebody just has a dry sink trap.

A failing drain field can also show up as unusually wet or greener grass in one area. That sign by itself is not enough for me to condemn a drain field, but when it appears with sewage odor and drainage problems, it means more.

Backups are much less ambiguous. If wastewater is coming into a tub or other fixture, or sewage is surfacing in the yard, I would stop trying home remedies and get the system checked. This is where I try to be practical with people. If the smell is only inside the house and there are no septic symptoms, I may tell them to call a plumber first. I do not want to charge somebody to open a septic tank if everything they are describing points to a vent or plumbing problem inside the house.

Pumping the tank can tell us much more than the smell can

Odor alone can be difficult to diagnose because gas moves through plumbing, vents, crawlspaces, and air currents. Once we are on the property, I would rather look at what the system is actually doing.

We start by checking the tank and the inlet and outlet areas for restricted flow, damage, or an abnormal liquid level. Pumping the tank can be one of the most useful diagnostic steps because once the liquid level drops, we can see more of the tank itself and watch what happens from the drain field side. If wastewater starts flowing back toward the tank after we pump it down, that tells us the downstream system is saturated or restricted and is not accepting effluent the way it should. We can also probe the drain field soil and check whether the area is unusually wet and whether the odor is coming directly from the ground. If the outdoor septic system checks out, then the investigation moves back toward the house. A camera can help us follow lines, and we document what we find with photos so the homeowner can see the same problem we are looking at. That documentation is important to me. If I tell somebody the problem is in the septic system, I want to be able to show them why. If I think the septic system is fine and they need a plumber, I would rather say that than invent a septic repair they do not need.

A few basic habits prevent a lot of odor calls

Rarely used drains should get water periodically so the traps do not dry out. A rocking toilet should not be ignored until the smell becomes unbearable, and grease is better kept out of the kitchen drain in the first place.

For septic maintenance, I generally tell homeowners to think in the three-to-five-year range for pumping, depending on the tank size and how many people are using the system. Waiting ten years because nothing appears wrong is not a maintenance strategy. In the Inman case, that long interval was part of the reason we found so much grease and solids at the tank. I also do not recommend garbage disposals for septic homes if you can avoid them. SCDES notes that they can add considerably more solids to a septic tank, which means the system may need attention sooner.

If the odor keeps coming back after you have run water through the unused drains, it is worth figuring out the source instead of covering it with another air freshener. A smell is information. Sometimes it leads to a ten-second plumbing fix, and sometimes it points to a septic problem that needs to be dealt with before it becomes a backup.

Homeowners dealing with recurring septic odors, drainage problems, or suspected tank and drain-field issues in Upstate South Carolina can learn more about troubleshooting and septic service at Rock Solid Septic & Excavation.

Expert Conversation with John (Ivan) Rusev

The Stone Magazine (TSM): John, when somebody says their house smells like sewage, do you assume it is septic?

John (Ivan) Rusev (JR): No. A lot of times it is plumbing. If they tell me there is a smell inside but they have no backup, no slow drains, and nothing wrong outside, I will usually tell them to talk to a plumber first.

TSM: What plumbing problem do you see most often on newer homes?

JR: Venting. The vent was not done right, something was missed, or it was not finished correctly. New construction can have septic odor without there being anything wrong with the septic tank.

TSM: What about homes with a pump system?

JR: The control panel can be part of it. If the conduit is not sealed correctly, gas can travel through where the electrical wiring comes in. Then the homeowner smells it inside and thinks the whole septic system is failing.

TSM: Is there any reliable way to tell from the smell alone whether it is plumbing or septic?

JR: Not really. If I see a wet area in the yard and it smells there, then obviously that gives me something to work with. But if all you have is a smell inside the house, that by itself does not tell me enough.

TSM: What can a homeowner safely try before calling someone?

JR: Run water into drains that have not been used in a while. That is easy, and if the trap dried out, it may solve the problem. Check whether a toilet is moving at the base too. I would not start opening the septic tank or messing with electrical panels.

TSM: When does the smell start looking more like a drain-field problem?

JR: If it is outside around the drain field and you also have wet ground, slow drains, gurgling, or problems after heavy rain, then I am paying much more attention to the septic system.

TSM: Why do you sometimes pump the tank during diagnosis?

JR: Because it tells me a lot. Once I lower the tank, I can look at the condition inside and see what happens from the drain-field side. If wastewater starts coming back into the tank, I know the drain field is not taking it like it should.

TSM: Does unusually green grass mean the drain field failed?

JR: Not by itself. I want more than one sign before I tell somebody they need a drain-field repair. Green grass and a smell, especially with wet soil or backups, mean more than green grass alone.

TSM: What is the biggest mistake homeowners make with sewer odor?

JR: Waiting and hoping it disappears. If it was just a dry trap, fine, that is easy. But if it keeps coming back, figure out where it is coming from instead of spraying something over it.

TSM: And what would make you tell someone to call immediately?

JR: Sewage backing up inside the house or surfacing in the yard. At that point, I would stop trying to diagnose it yourself and get somebody out there.