How to Get Rid of Septic Tank Smell -Outside & Inside

It is normal to have a sewer smell inside a septic tank. The smell should however be contained inside the septic tank and should not leak outside or inside the house.

Anaerobic bacteria break down organic waste inside the septic tank which results in production of carbon dioxide, methane and hydrogen sulfide gases. Hydrogen sulfide gas is the most noticeable since it smells like rotten eggs.


A smelly septic tank is a sign that the septic tank is full, the lid is not sealing properly or that the plumbing vent is not functioning properly. It could also be caused by a reduction of bacteria in the septic tank resulting in untreated sewage being dumped in the drain field.

Depending on the cause of the problem, septic tank smells can be experienced in the following areas:

  • Near the drain field
  • In the yard
  • Around the septic tank
  • Inside the house

To stop your septic tank from smelling, have it emptied if it is full, replace the lid if it is no longer sealing, or have the plumbing vent unclogged, extended or fitted with a carbon filter. You can also introduce biological additives (enzymes and bacteria) in the septic tank to prevent untreated waste from flowing to the drain field.

In some instances, you could be dealing with a leaking sewer line. This is the underground pipe connecting your house to the septic tank.

When raw sewage leaks, it percolates through the ground and when the temperature outside is warm, it starts to stink horribly. It is usually very hard for a homeowner to know if indeed that is the problem.

In a few instances, a leaking sewer line will be indicated by soggy spots in the yard or unusually green patches of grass. Sometimes there will be no sign which is bad since leaks are hard to see even with a sewer inspection camera.

High acidity can also cause a septic tank to smell. Adding a septic tank odor neutralizer helps to balance the PH inside the tank and therefore get rid of the smell. At home, pouring a cup of baking soda (alkali) in the toilet or sink drain will lower the septic tank’s acidity.

Let us now look at the various ways to get rid of septic tank smells in and around your house.

Inside the House


Inside the house, septic tank smells will be experienced in the bathroom (since that is why you have most drains), the basement or sometimes the kitchen.

The way your house is designed, waste is supposed to flow out of the drains and out into the septic tank via gravity. Sewer gases are then channeled out of the drain lines through the plumbing vent.

A plumbing vent is the vertical pipe which runs through the roof of the house. It is connected to the main house drain line where all the other fixture drains lines drain their waste.

To ensure that indeed sewer gases flow out through the plumbing vent and not fixtures drains, their drain line have a U-bend known as a P-trap or. You can see it under your bathroom or kitchen sink.


The Drain trap, as it is also called is what allows you to have water at the bottom of the toilet bowl at all times. P-traps in sinks, tubs, showers and washing machines not forgetting the basement floor drain are also full of water.

The water acts as a barrier which is what blocks sewer gases from coming in to your house.

If a particular drain has not been used for some time for instance the guest bathroom sink or shower, the water in the P-trap will evaporate. When that happens, the barrier will be broken and septic tank smells will waft through the drain and into your house.

To fix this problem, pour some water in drains that you have not used for a while and the problem will be fixed. Make it a habit to do this on all your drains when you come back from vacation and flush all toilets as well.

Another thing that can remove water from your P-trap is a clogged plumbing vent. Apart from removing sewer gases from the house, the vent also introduces air into the drain lines allowing them to drain fast.

When a plumbing vent is clogged, a negative air pressure will be created inside the drains. This is why you will hear your bathtub/shower drain gurgling after flushing the toilet.

What happens in that case is that a vacuum is created inside the drain line which siphons the water in the P-traps and hence the gurgling noise. With an empty P-trap, septic tank gases will be all over your house.

A leaking P-trap or a toilet wax ring that is not sealing can also bring about the septic tank gases. If that is the case you will need to replace the P-trap or toilet wax ring.

The first thing to do however is to climb to the roof of your house and unclog the plumbing vent. I have written a detailed article on how to do exactly that. Read it here.

If you have an ejector sump pump, check if the basket is properly sealed as that can also result in sewer smells. If it is leaking apply a new seal on the cover to prevent more leaks.

Outside House Near the Septic Tank


If the septic tank smell is concentrated near the septic tank, the problem is restricted to the septic tank. Either the lid is not sealing properly or the septic tank is full resulting in ineffective waste breakdown.

Let us start with lid that is not sealing properly.

To troubleshoot a septic tank, you must first be able to locate it. Most septic tanks lids are usually buried under mulch and there not very conspicuous. Check out this post to help you locate your septic tank.

Septic tank lids are made from concrete, metal or plastic. While metallic lids are heavy and can last for a long time, concrete and plastic lids can fail and start to leak.

If that is the problem you have, go ahead and replace the old lid with a new plastic lid with a rubber seal. This helps to contain the septic tank smells inside the septic tank.

If you have a concrete septic tank lid and you are looking for a temporary fix, you can use weather stripping to create a seal that should do the job until you replace the lid.

The main reason however why you may be having a sewer smell close to your septic tank is because the tank is full and has not been emptied.

Ideally, a septic tank should be emptied once in 3 to 5 years. The frequency depends on the size of the tank, the household size and the amount of wastewater generated.

But how do you know that your septic tank needs to be emptied? The telltale signs that it is time to empty your septic tank include:

  • Slow drains
  • Standing water in the drain field
  • Sewage backups
  • Sewage odors
  • Gurgling drains
  • Green patches of the lawn
  • Weak/slow flushing toilets.

I have written a detailed guide on the above signs in a separate article. Read it here.

In a septic tank, the solids after being broken down by the bacteria will form a sludge and settle at the bottom of the tank. As the sludge accumulates, it will need to be emptied before it reaches the tank’s outflow pipe.

The sludge and untreated waste water can flow out to the drain field and result in sewage smells or even clog it.

In the Yard

If there is a sewage gas smell in your yard, the problem points out to a faulty plumbing vent or a leaking sewer line.

Starting with the sewer line, inspect if the sewer cleanout plug is tight. A loose plug on the sewer cleanout can allow sewer gases to exit through it.

A sewer cleanout is a pipe (about 4 inches in diameter) sticking a few inches from the ground usually located very close to the house. It will most likely have a plug with a square nut at the top.

Tighten the plug if it is loose or replace it altogether if it is broken.

As I already mentioned, it is very hard to tell if you have a leaking sewer line unless there spots in your yard which are soggy or where there are sink holes.

If you house is constructed in a forested or low-lying area like a valley, its location affects how the plumbing vent works. Instead of sewer gases flowing away from the house, wind currents will blow the smell towards your yard and hence the septic tank smell outside your house.

There are 2 things you can do about this problem. The first one is to have the plumbing vent extended. An extended vent will make sure that the sewer gases are driven further away from the house.


The other method is to install a carbon filter on top of the plumbing vent. The filter will remove sewer gases before exiting the vent stack but will need to be replaced annually or sometimes after 5 years.

Good carbon filters will remove the sewer gases but at the same time allow air to flow into the drain lines. If the filter completely blocks the vent you will have slow drains and weak flushing toilets.

From the Drain Field

If there is a strong sewage smell coming from the drain field, it means 2 things:

  • The septic tank is failed or is failing
  • You need to empty your septic tank

As I mentioned, if you don’t empty your septic tank when you should, the sludge level will raise and where it reaches the outlet pipe, the sludge as well as fresh wastewater from the house will start flowing to the drain field.

The organic decomposition of the waste is what will result in the sewage gas coming from the drain field.

That is also the same thing that happens when the septic tank fails. A failing or failed septic tank means that the bacteria cannot break down the waste from your house resulting in the same being sent to the drain field without being broken down.

Usually, a failed septic tank is caused by harsh chemicals. If you use bleach, sulfuric acid and other chemical drain cleaners, they will kill the bacteria in the septic tank and when that happens there will be no microbes to break down the organic waste.

One solution to this is what is called shock treatment. In shock treatment, biological additives that are made from enzymes and bacteria are introduced in the septic tank to replenish the already depleted microbes.

The thing with a failing septic tank is that some solid waste can find its way into the drain field and clog the pipes. As such, you may want to bring an expert to inspect the entire system and recommend the best solution.

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