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Homeowners often call us with concerns about strong sewer odors suddenly occurring in their houses. They immediately assume there may be a problem with their septic system, but most of the time, that is fortunately not the case. Here are a few of the most common causes and what can be done about them.


Most of the drains in your home like sinks, showers, tubs, washing machines, and floor drains, have a simple mechanism known as a P-trap. P-traps are curved, U-shaped pipes designed to always have a small amount of water resting in the bottom. This water provides a vapor barrier that keeps sewer gasses from rising back up through the drains and into your home.

If your house has been vacant, or if you have an extra bathroom that no one has used for a long time, the P-traps can dry out, allowing sewer gases to escape into the house.

This has an easy solution: Simply run water in all drains periodically to ensure there is always water in the P-traps. If you’re going to be gone for several weeks or months, you can also add a teaspoon of vegetable oil to the drain – just enough to form a thin layer on top of the water in the P-trap. This oil layer will protect the water from evaporating and easily break up when the drain is used again. Just don’t overdo it!

Once you have rehydrated the offending P-trap, the odor should dissipate after a day or two. If it continues to come from a specific drain, remove the grate, clean the drain, and use disinfectant to kill any lingering bacteria.

Toilet Flanges

When a home is built, flanges are installed on the surface of the bathroom floors to which toilets are bolted. A thick wax ring is then used to seal the base of the toilet against the flange.

Interestingly, toilets are different than any other drains in the house, in that they have straight pipes instead of P-traps. This is because the toilet’s construction is already designed like a P-trap. So assuming there is water in the bowl and tank, the only place that could be leaking sewer odors is at the flange. There are two common scenarios for this:

The first is that, after many years of use, the wax ring will slowly dry out and begin to crack. The toilet won’t leak at the base when you flush because it’s shaped like a funnel and hovers over the flange. You may notice small water leaks at the same time, but usually only if the plumbing backs up. The sewer odors, however, are a gas and will begin to escape between the flange and the toilet. Replacing the wax ring is a very easy and inexpensive fix you can do yourself, which should take care of any odors.

The second is when homeowners decide to upgrade an old bathroom and install new tile flooring without taking into account the difference in thickness from things like backer board, cement, and tile. In some instances people have added nearly a full inch to the height of the floor. If the flange is still where it was originally, there will be a gap where vapors can escape.

The remedy is to install a jumbo wax ring, which is on the same shelf in your hardware store and costs just a fraction more than the standard wax ring. This will fill in that extra gap, give you a good seal at the base of the toilet, and should eliminate your odor problem.

Sewer Vents

Every home has a ventilation system specifically for the sewer plumbing. Its purpose is to equalize the atmospheric pressure caused by wastewater running through the system in order to allow sewer odors to escape and take fresh air in. If these vent pipes are somehow blocked, odors can’t be released outside and can build up inside the pipes, eventually seeping back into your home.

Sewer vents are typically small, uncovered pipes sticking up through your roof. These can become obstructed over time, often by years of dust and dirt buildup, but also by plant debris or even small bird nests. The main sign that you have one or more blocked vents is if all your plumbing fixtures are slow to empty and your floor drains make gurgling noises or air bubbles as they try to drain.

Climbing up to the roof and inspecting all the vent pipes with a bright flashlight will usually reveal the problem. Most blockage can be cleared out by running a garden hose as far as you can down and back up the pipe while washing it out with water. If you do this yourself, we recommend you work cautiously and have someone with you to help, as climbing a ladder and walking around on a roof can be dangerous.

Septic Tank

If you are still experiencing sewer odors in your house after ruling out the easy and inexpensive solutions above, it’s time to consider that your septic tank may need to be pumped out.

In addition to fowl odors entering your home, other early signs that your septic tank needs pumping include excessively lush, green grass above the tank and/or drain field and water pooling on the surface. If this is the case, contact your servicing company immediately.

A full septic tank can send solid waste into the drain field, clogging leach-field pipes. With no place to go, the wastewater seeps out of the tank and pipe joints in the drain field and rises to the surface. The septic tank eventually becomes so full that it cannot accept any more wastewater, resulting in a backup of black, foul sewage into the toilets, sinks, and bathtubs in your home.

The sooner you take care of a full septic tank, the less expensive (and disgusting) it will be.

Sewage Pump

If your septic tank is positioned at a lower elevation than your drain field, your septic system will require a sewage pump to work against gravity and move wastewater from the tank to the lateral lines.

If your septic system requires a sewage pump, then a full septic tank could be the result of a faulty pump or a short in the pump’s electrical relay, especially if you have had your tank serviced recently enough that it should not already be full again. While your septic technician is at your home, make sure he or she also inspects both the pump and electrical relay to ensure they are working properly.

Drain Lines

In some cases, the sewer drain lines may have developed a crack or become broken. This can cause sewage to be released right under your home instead of being carried away. While a broken or damaged drain line is generally rare, it can happen with age, faulty materials, invasive tree roots, or earthquakes.

If you’ve gone through every step listed above, and you haven’t discovered a problem with your P-traps, flanges, vents, septic tank and/or sewage pump, then you will need to call a licensed plumber to inspect and likely replace one or more of your drain lines.

Unfortunately, this could be very expensive, so you want to make sure you’re working with someone who is experienced and reputable. Give Yoder Septic a call and we will gladly send you a short list of local plumbers whom we work with on a regular basis and highly recommend.

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