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Do Septic Tanks Smell? (A Guide for Homeowners)

Do Septic Tanks Smell? (A Guide for Homeowners)

If you’ve never lived in a home that had a septic tank then you may find yourself wondering if they smell! This is especially true if you’re looking to purchase a home that has a septic tank and don’t want to find yourself in a stinky situation.

Well-installed and properly-maintained septic tanks should be odor-free. Nevertheless, it’s not unusual to notice odor problems with a septic system. Weak-smelling odors surrounding a septic tank are perfectly normal, considering there’s the decomposition of organic waste taking place.

While some septic tank odors are normal, others may be indicative of a serious problem. Knowing the difference between normal and abnormal septic tank smells can help you know when to ignore and when to call a septic tank professional.

What Does a Septic Tank Smell Like?

When we talk of a septic tank, the thought of foul smell suddenly comes to mind. When septic odors are lingering around a home, the first sign a homeowner notice is the smell of rotten eggs.

If the area surrounding your septic tank smells like rotten eggs, then it is hydrogen sulfide filling the air.

Hydrogen sulfide gas results from decomposing organic material, and it is one of the many compounds that make up the gas found in sewage.

Why Do Septic Tanks Smell?

Your sewage treatment and disposal unit may emit some odors from time to time.

However, if you notice an overpowering and persistent smell wafting from the direction of your septic tank, it may be a sign that something’s wrong!

With that in mind, here are some of the most common reasons what a septic tank might develop an unusual odor.

Insufficient Bacteria

Inside a septic tank, bacteria work to break down waste solids. For the bacteria to survive and do their job, the pH level must be sustained between 6.8 and 7.6. If the pH is lower, it becomes acidic, which kills the bacteria inside your septic tank.

Other than a low PH, insufficient bacteria in the tank can result from the temperature, nutrient availability, and oxygen content within the tank being out of balance. When any of these imbalances occur, a strong hydrogen sulfide gas tends to develop.

If you are using strong detergents and chemicals in your household, you will also likely harm the bacteria population inside your septic tank. Detergents and chemicals can kill bacteria, thus stop the digestion of waste.

Avoiding or minimizing the use of strong detergents and chemicals can help maintain the required amount of bacteria inside your septic tank and prevent awful smells.

Septic tank smell as a result of insufficient bacteria is also common in newly installed and recently pumped out septic tanks. You can restore the bacteria population in your tank by adding bacteria additives into your septic tank.

Once there are sufficient bacteria in the tank, the foul smell will most likely disappear. However, it’s worth pointing out that the use of additives are rarely the answer for a full-time residence.

Make sure to take a look at my article on are septic tank additives necessary for more info on this topic.

The Tank is Full

When working properly, septic tanks are designed to operate for years without any human intervention. A septic tank only needs emptying when the solid waste levels have mounted up within the tank.

Depending on the number of people in a household, septic tanks generally need to be pumped every couple years. As your septic tank fills up, you will notice a number of issues, one of them being odor emanating from your outdoor septic tank, toilets, and drains.

If you have not had your septic tank pumped out for years, then you should get a septic tank specialist to check how full your tank is.

Broken Seal or Connection

Your toilet has a wax ring at its base, which helps keep a seal between the toilet and the drain pipe.

When that seal is broken, it can allow sewer gas from your sewage tank to leak through your sewer pipes.

If you’ve noticed a septic tank smell from your toilet, then you should have a plumber check the toilet wax ring.

Blocked Ventilation

While septic tanks should be airtight, they should be sufficiently vented. Vents should be fitted in an area where there is an excellent airflow to diffuse any odors that may originate from the septic tank.

You can also fit your vent stacks with carbon filters to regulate smells from your septic tank.

Food Waste

Once we take food, our bodies break down and absorb its nutrients, releasing only waste tour septic tanks.

Generally, septic tanks are designed to break down and digest body waste. If you allow a lot of food waste to go into your septic tank, you will most likely have a smell issue.

Is Septic Tank Smell Dangerous?

Septic tank smell is not necessarily dangerous at low levels. Nevertheless, prolonged exposure to high levels of sewer gas can be hazardous.

The reason why septic tank smell is dangerous is that it contains a complex mixture of various compounds and gases, some of which pose some danger level. In small amounts, these gases may not be dangerous.

However, at high levels, these gases can contribute to sewer gas toxicity, presenting several problems. The following are the toxic gases and the threat they pose:

• Hydrogen sulfide: This is the primary gas in septic tanks. In high amounts, hydrogen sulfide gas has been toxic to the body’s oxygen systems and can cause adverse health issues.

• Ammonia: This is a compound that is usually used in cleaning chemicals. Exposure to ammonia gas can cause nose, throat, and eye irritation. Prolonged exposure to high levels of ammonia can cause organ damage.

• Carbon dioxide: Exposure to high quantities of carbon dioxide gas can trigger various health issues, including headaches, difficulty breathing, increased heart rate, high blood pressure, and asphyxia, among others.

• Methane: While methane is relatively a nontoxic greenhouse gas, it is extremely flammable in large amounts. Paired with ammonia’s flammability, the mixture makes high levels of septic tank smell a fire hazard.

Depending on other factors such as humidity and weather conditions, mold spores may also be present in sewer gases. Therefore, it is crucial to have your sewer tank inspected and the odor problem addressed as soon as possible.

What Are the Signs That Your Septic Tank Is Full?

While septic tanks are low-maintenance, they still need to be inspected regularly and occasionally emptied to keep them in full working order.

The following are the signs that your septic tank is full and needs to be drained:

Bad odor

As previously mentioned, you are likely to notice a foul odor when your septic tank is full.

Therefore, a bad smell is one of the signs that your tank is at its maximum capacity and needs to be emptied.

Pooling water

If it has not rained lately and you are seeing pools of water forming around your septic tank drain field, this is a sign that your septic tank is overflowing.

A congested or overflowing septic tank will force liquid up to the top of the ground, forming water pools on the ground nearby.

(Overly) Healthy lawn

Does the grass above your septic tank healthier than the grass growing in other areas of your home?

If so, your septic tank could be behind it. The logical explanation is that water is coming out of your septic tank, which means it’s either leaking or full.

Slow drains

Slow-flushing toilets and water taking a bit longer than usual to drain from the bath or sink are common indicators that the septic tank is full.

Since slow drains are also indicative of a clog in the septic system, it is important to have a plumber take a look at the system to diagnose the problem.

Sewer backup

This is a sign that’s hard to miss. It usually occurs when your main sewer lines or drain pipes are clogged or when the septic tank is full. Be sure to keep an eye on your drains!

If they show signs of backing up, you need to have your septic tank emptied as soon as possible.

Conclusion on Septic Tank Smell

The importance of a septic tank cannot be overemphasized. If your home is not connected to a municipal sewer system, it is almost impossible to survive without a functional septic system.

When there is a significant problem, such as overpowering the septic tank smell, you should have a professional inspect your tank to take the best cause of action.

Lindsay Reed

Hi, I'm the founder of! I created this website to be a resource for everyone who wants to make the best home possible.