Why Does My Septic Tank Smell

Why Does My Septic Tank Smell2019-07-31T00:38:27+00:00

Why does my septic tank smell?

As septic tanks receive waste from the toilet, some very repulsive odors can generate from them. This can make daily living in your house unpleasant and can be downright embarrassing if you’re hosting a party or if friends drop in.

Should my septic tank smell bad?

Although there are occasional odors from septic tanks, your septic tank should not be stinking on an ongoing basis. In a healthy system, the septic tank receives waste from the toilet flushes, allows the solids to sink down in the tank, gradually forming sludge, while allowing the liquids to flow out into the distribution trenches. A septic tank in ideal condition contains bugs and bacteria which help to break down and “eat” the solids. To find out more information about how a septic tank works, visit our information page on Maintaining and Cleaning Septic Tanks.

How can I stop my septic tank from smelling?

If your septic tank stinks, firstly identify exactly where the smell is coming from. Is it a bad smell wafting around outside? Is the smell coming up from the toilet? Does it only stink outside around the actual septic tank?
There can be a variety of issues which cause septic tanks to smell and finding the source of the odor can narrow down the septic tank stench problem. Below are some of the main issues causing the septic tank to smell:

My septic tank toilet is stinking
The first cause of a smelly septic tank is if the tank is full and needs pumping out. In this case, please contact us to book in your septic tank pump out. Lee’s Environmental provide the highest quality septic tank pump out service on each occasion – please see our Septic Tank Cleaning page for more information.

If you’re already having your septic tank cleaned out regularly, but bad odors are coming up from the toilet pipe into the toilet bowl, this usually indicates there is a problem with the bugs and bacteria in the septic tank where they have been disrupted and are beginning to die off. You can encourage the bacteria to repopulate with the following method:

  • Get a cup of regular raw or brown sugar from your kitchen.
  • Flush it down the toilet.
  • Repeat once a week for 6 – 8 weeks.

If the smell continues to be an issue, you will need to take further action. First, try a hydrated lime solution which neutralises the PH levels in the tank and creates a film over the top that dampens the smell:

  • Buy a 5kg bag of hydrated lime (can be found at Bunnings and similar stores).
  • In a large 10L bucket, mix 5kg of hydrated lime and fill the bucket to the top to create a mix of 50% hydrated lime with 50% water.
  • Flush the equal parts hydrated lime and water mixture down the toilet

Wait a few days to check if this has taken care of the smell. If you still continue to experience bad smells from the toilet, you may need to have the septic tank pumped out to reset the bacteria in the tank. Please see our Septic Tank Cleaning page or Contact Us to book your service.

Bad smells are coming from around the septic tank
If the stench seems to be coming from outside where the septic tank is located, there may be a hole in the septic tank lid or the septic tank lid may not be sealed properly. Lee’s Environmental can provide replacement of your lids – please visit our Maintaining and Cleaning Septic Tanks for more information.

My house has a septic system and there is a bad odor somewhere outside
If there is a bad smell wafting around but doesn’t seem to be coming up from the toilet or from the septic tank, it may be something else on your property that smells. Most properties that have a septic tank also have a grease trap which receives waste from the kitchen sink and greywater tank which receives waste from the laundry and showers. Either of these tanks could be causing a bad odor and the stench from a greywater tank is often mistaken for a stinky septic tank. If you think one of these tanks may be causing the smell, please see our pages Why Does My Grease Trap Smell and Why Does My Greywater Tank Smell.

If your grease trap and greywater tank are being maintained regularly and them smell doesn’t seem to be generated from them, the distribution trenches may be causing the smell. Distribution trenches, also called transpiration trenches or drain fields, receive the liquid parts of the waste from the septic tank, grease trap and greywater tank. If there are areas on your yard where grass is always growing prolifically or areas of your property that are always wet, this indicates that the trenches are saturated, blocked or have failed. If you’re experiencing trench problems, Lee’s Environmental offer high pressure drain cleaning called jet rodding which has an 85% success rate of clearing blockages. To find out more about this service, please see our Drain Cleaning page.

Can septic tank smells be prevented?
Most septic tank smells are preventable by using the right cleaners, only flushing the appropriate items down and toilet and cleaning the tank as needed. Here’s our recommendation to keep your septic system smelling sweet:

  • Only use 1 or 2 ply toilet paper
  • Never flush nappy wipes, sanitary napkins, condoms, kitty litter or other items down the toilet
  • Do not flush wipes marketed as “flushable wipes” or “bio-degradable” down the toilet as these do not break down quickly enough and will cause a crust to form on the tank and can cause blockages
  • Repair leaking toilets
  • Install a dual-flush cistern for the toilet
  • Clean your toilet with natural products – see our Septic Toilet Cleaning Recipe
  • Pump out the septic tank every 2-5 years when the sludge levels reach 30%. Lee’s Environmental provide free sludge testing when on your property to clean your grease trap and or greywater or if we’re in your area on a neighboring property. Please see our Septic Tank Cleaning page for more information.


Please note that there are a few occasions where the bacteria in the tank will inevitably begin to die off:

  • When a person using the toilet is on certain medications such as antibiotics
  • If a person using the toilet is currently undergoing chemotherapy

In these cases, the septic tank will need frequent pumpouts to maintain it. Lee’s Environmental can put your property on regular scheduled servicing so you don’t need to worry about the septic tank through these times. Please call our office on 3206 4844 to discuss your needs with our friendly staff.

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