Septic Tank Treatment & Maintenance Products, What No One Is Telling You


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Can Additives Improve Digestion in a Septic Tank?

Do septic tank additives really work, and are they necessary to the health of your septic system? Can additives save your septic system or help efficiency?

It is well known that in order to extend the life of a septic system it needs to be well maintained. But does this maintenance include adding additives to your septic tank? More importantly, will additives help to aid digestion and dissolve solids, thereby helping to prevent clogging, reducing the frequency of having the septic tank pumped out and keeping your system operating reliably as manufacturers of these additives would like us to believe? And how effective are other methods commonly employed before septic tank additives were invented? This article will address some of the common misconceptions and fallacies surrounding the use of septic tank additives. To do this we first need to understand how a septic tank works, then we need to look at the different types of additives and investigate the effects of each type, and the impact (if any) they have on the system.

How a Septic System Works

The primary reason why homeowners believe they need to use additives in their septic system is that they don’t fully understand how a septic system works. A septic system by design uses natural biological processes to break down the waste and doesn’t require any human assistance, biological agents or chemical additives to speed up the process. In fact, trying to speed up the process can do more harm than good, as we will soon discover.

The wastewater and solid waste that flows into your septic system from your home contain anaerobic bacteria — bacteria that live in an oxygen-free environment — that is fundamental to the breakdown process. Once the waste reaches the septic tank, the bacteria jump into action, breaking it down, helping to separate it into layers. The solids sink to the bottom of the tank forming a layer of sludge, while fats and oils float to the surface where they form a layer of scum. This leaves a layer of partially clarified liquid wastewater known as greywater or effluent sandwiched between the two. The liquid effluent flows into the soil absorption area of the drain field, where it is further treated by natural biological, chemical and physical processes that occur within the soil.

how a septic system works

The whole breakdown process is designed to occur naturally, and if the system is not overloaded and the bacteria are left alone to get on with their job in peace, they do so very efficiently. Unfortunately, human nature being what it is, we like to think we can improve the workings of nature; but inevitably we just end up putting a proverbial spanner in the works. Septic tank additives are manufactured and marketed in the hope that they will solve common problems that homeowners encounter with their systems, but invariably these problems are caused by poor system design, improper use, poor system maintenance (not pumping the tank out regularly), or a combination thereof. While some septic tank additives can be beneficial under certain conditions, most are ineffective and serve no purpose at all, and in worst-case scenarios, they can actually be detrimental to the natural biological processes taking place within the system.

Different Types of Septic System Additives

Septic tank additives are typically added to a septic system in order to help break up the layer of surface scum, speed up the digestion of the settled sludge (biosolids), or to provide a quick fix remedy to clear and restore a clogged drain field. In the majority of cases, additives are used to aid digestion of solid matter inside the septic tank, breaking it down into liquid or gas form and finer solid matter that settles more readily or to boost ailing bacterial populations that have been decimated by toxins (bleach, antimicrobials, antibiotics, etc) present in the system.

different types of septic tank additives

Septic tank additives are generally classified into two categories:

  1. Biological additives, including bacteria, enzymes and yeast that boost biological activity within the system;
  2. Chemical additives composed of both organic and inorganic compounds that are typically used to control odours, to reduce solids or to restore a clogged drain field.
different types of septic system additives

Considering that there are currently around 1,200 commercial septic tank additives on the market, when it comes to maintaining our septic systems, it appears we are clearly spoilt for choice. But is purchasing these products money well spent or are we literally throwing money down the drain?

Biological Septic Tank Additives

The jury is still out as to whether biological additives offer any beneficial effects to a septic system, with scientific studies offering conflicting conclusions in this regard.

One scientific study has identified two potential benefits: 1) Enzyme-based additives may be able to reduce the amount of fat in a septic tank; and 2) In septic tanks that have experienced a die-off of bacteria as a result of toxic chemicals such as drain cleaner, bleach, anti-microbial agents or antibiotic medications being present in the system, biological additives can help boost bacterial populations and reduce solid matter in the tank effluent.

septic tank treatment

However, another study suggests that certain biological additives could stimulate biological activity to such a degree, causing methane gas that forms during the anaerobic decomposition process to bubble up, which in turn forces solids from the bottom layer of sludge up into the greywater effluent, enabling solids to flow out into the drain field where they can clog up the soil absorption area.

It is also believed that rather than reducing the fatty layer of scum (which cannot escape when floating on the surface), enzyme-based products effectively disrupt and break up this layer of fat, enabling it to flow out of the tank with the effluent where it can cause clogging problems in the drain field.

Adding Bacteria ‘Starter’ Cultures to Your Septic System

There are times when the natural bacterial communities living in the septic tank may be decimated by careless practises or may die off due to unavoidable circumstances, including after:

  • chemical treatment with drain cleaners, solvents or antibacterial agents;
  • heavy household use of antibacterial soaps/detergents/cleaning agents;
  • extensive or prolonged use of antibiotics;
  • the holiday home has been uninhabited for six months or more.

While there are bacteria ‘starter’ products on the market that will replenish the bacterial communities in the tank and rejuvenate the system, these are not really needed for the reasons discussed below.

Firstly, estimates of bacterial die-off in septic tanks — which show that around 2 gallons (7.5 litres) of bleach would most likely harm bacterial communities living in the tank —  have been calculated using a static septic system with a fixed volume that has no additional sewage or wastewater entering the system. Consequently, these calculations fail to take into account the fact that the addition of new wastewater effluent and sewage would dilute the contents of the septic tank and reinoculate the system with bacteria. The smaller quantities of bleach and drain cleaners that most households would normally use is not likely to harm a healthy septic system.

Secondly, if you don’t address and fix the cause of the die-off, no matter how much bacterial starter you throw into your tank the problem will persist because the new bacteria will also be killed by whatever killed your initial bacterial community if it is still being added to the mix. As soon as you refrain from adding harmful chemicals, disinfectants and/or antibiotics to the system, the tank will be reinoculated with natural bacteria when human waste is flushed down the toilet. There is no need to purchase a starter culture to add bacteria to the system.

Organic Solvents and Inorganic Compounds in Your Septic System

Chemical additives in your septic system, such as hydrogen peroxide, sodium hydroxide (caustic soda), sulfuric acid and commercial drain cleaning products that typically contain these chemicals, are often used in septic systems to clear clogged pipes or to unclog a drain field. Yet these chemicals are extremely harsh and can actually damage the system rather than fix it. Hydrogen peroxide, for example, can agitate fine particles in clay and loam soils, disrupting the soil structure, which in turn reduces soil permeability. Sulfuric acid, the key ingredient in many commercial septic system products, is extremely corrosive in its concentrated form and can not only negatively impact the bacterial colonies that are hard at work in the septic tank and drain field but can also weaken the structure of a concrete tank.

septic system solvents

Chemical Additives that Control Odours in Your Septic Tank

Commercial chemical potions that are marketed to address odour problems typically contain formaldehyde, quaternary ammonium, and zinc sulfate as their active ingredients. They combat odour by controlling the growth of anaerobic bacterial communities, or more specifically, by targeting bacteria in the septic system. Considering that these bacterial communities are the workforce that forms the backbone of a healthy septic system, this is not just counterproductive, it is also extremely destructive. Use of these products can result in an unbalanced system that at best do not function efficiently, and in a worst-case scenario can lead to complete system failure.

Are Organic Solvents, Degreasers, Deodorizers, and Sanitizers Safe For Your Septic System?

Organic solvents usually containing chlorinated hydrocarbons are typically used in degreasing agents that are marketed to break down grease and oils. Commercial products used to clean and deodorize portable toilets also often contain organic chemical compounds such as alkanes, benzenes and naphthalenes. These organic solvents are significant environmental pollutants and should not be used in a septic system as they can escape into the environment and contaminate groundwater.

organic septic friendly solvents

Old Wives Remedies

Adding Yeast to Treat a Septic Tank

The bacteria that live in the septic system are not made up of yeast, nor do they eat yeast, so adding yeast does nothing to boost their efficiency. While one may think that yeast would be harmless to a septic system, it causes frothing and agitates the contents of the tank, preventing the solids from settling to the bottom of the tank and fats from coagulating on the surface. This results in solids escaping to the drain field where they can clog soils and shorten the lifespan of the soil absorption system, resulting in the need for expensive repairs.

adding yeast to a septic tank

Adding Baking Soda to a Septic Tank

Baking soda, along with other products marketed as flocculants are purported to promote the clumping of particulate matter, thereby reducing the concentration of suspended solid particulates in the greywater effluent within the septic tank. If this were true, it could theoretically improve the quality of the effluent discharged from the septic system. However, there is no proof to suggest that baking soda can improve the rate of flocculation, as it would no doubt require adding vast quantities, which could, in turn, upset the chemistry (for example, the pH) in the system, negatively impacting the bacterial communities that are essential to a healthy, properly functioning system.

What About Adding a Combination of Yeast and Baking Soda?

A question that sometimes arises is whether one can use yeast to agitate the sludge together with baking powder to reduce the concentration of suspended solids in the greywater effluent, or would they just neutralize one another? As mentioned earlier, it is not a good idea to add yeast to your tank in the first place. Adding baking soda in the hope that it will magically neutralize the effects of the yeast will leave you back where you started, with neither having any positive effect on the system and a good chance that you will kill off the bacterial communities while you are at it. If on the other hand, the baking soda fails to neutralize the effect of the yeast, which is very likely, it is serving no purpose at all other than adding unwanted chemicals to your tank that could potentially negatively impact your system.

Adding a Dead Chicken, Raw Meat or Roadkill to Boost Bacterial Action in Your Septic Tank

A common urban legend that has been passed down over the years is that tossing the carcass of a chicken or other dead animal into a septic tank will boost bacterial activity within the tank, improving the rate of digestion, which in turn will reduce the need to have the septic tank pumped out. The method behind the madness with regards to this old folklore is that adding dead chickens/animals or raw hamburger/liver etc to the tank will either add bacteria to the system or provide a source of food to encourage the growth of bacterial colonies living within the system. The reality is that bacteria is added naturally with human waste that enters the system, and that waste also provides all the food those bacteria need to survive. Also, the bacterial communities that naturally occur within the tank are made up of anaerobic bacteria, whereas flies, maggots and most of the bacteria that will typically colonize a carcass need oxygen to survive and are likely to die off once they reach the oxygen-free environment inside the tank. Adding any additional bacteria or food to stimulate biological activity in an effort to speed up the rate of decomposition is likely to have the opposite effect and will only overburden the system and contaminate the groundwater with bacteria-laden effluent. So please don’t go wasting a perfectly good chicken by dumping it in your septic tank. Either let it continue to run around happily contributing to your daily supply of eggs or donate your surplus meat to a charity that feeds those less fortunate.

How to Keep Your Septic System Additive-Free

Many homeowners instinctively opt for septic tank additives in the hope that they will keep their system running efficiently and extend the time between pump-outs, as well as extend the life of their system. Others purchase these additives in the hope that they can save their failing system. The truth is they can’t. But fear not; there are measures you can take to keep your septic system functioning efficiently that don’t involve using additives. Heeding the advice below can save you money that you would otherwise spend on additives, frequent pump-outs, or unnecessary costly repairs to your system.

Tips for Keeping Your Septic System Working Properly without Additives

  • Reduce your water usage by repairing any leaks and by installing water-efficient plumbing fittings wherever possible. Only run the dishwasher and washing machine when you have a full load. This will not only extend the life of your septic system, but it will also reduce your water and energy costs, saving you money.
  • Keep harsh chemicals and other toxins out of your system. Ensure that any unused paint, varnish, solvents, petrochemicals and pesticides are disposed of responsibly at a local garbage or recycling depot that handles these materials appropriately.
  • Never flush solids such as cigarette butts, kitty litter, feminine hygiene products, tissues, paper towels or unused medications down the loo. Most take a long time to break down, overburdening your septic system, while medications could harm the bacterial communities living in your septic tank.
  • Don’t pour fat and grease down your kitchen sink.
  • Use a garbage disposal system sparingly as this adds to the volume of solids and water entering your tank, which will mean you will need to have your tank pumped out more often.
  • Wash smaller loads of clothing over the course of the week rather than overloading your system with a week’s washing on ‘wash day’.
  • Divert stormwater runoff and water from drainage away from your septic tank and drain field. Gutter downpipes and rainwater from rooftops should be channelled away from your septic drain field to prevent additional water entering the system.


Using septic tank additives will not compensate for a poorly designed system, regular system maintenance and inspection, and having your tank pumped out every 3-5 years or as needed. In fact, in some jurisdictions where the municipality has concerns regarding the impact on groundwater, building codes prohibit the use of septic tank additives, drain cleaners, degreasers, root killers, etc all together.

There is no need to throw chemical or biological additives, raw meat, dead chickens or roadkill to stimulate digestion. Harsh chemicals such as sulfuric acid and caustic hydroxides should never be used in a septic system as they can kill the bacterial communities living within the tank, cause the soil in the drain field to become less permeable, and can leach into the environment and contaminate groundwater sources.

If you have a well-designed septic system that is properly operated and maintained, bacteria will be added to the system naturally with the human waste that enters the system. These naturally occurring bacteria get all the food and nutrients they require from the waste that’s in the tank. There is no need to add more bacteria, nor do you need to add anything to feed them or stimulate their activity. By adding more bacteria without adding any additional waste, the bacteria will either die off as there will be insufficient food to sustain the artificially enlarged colony, or they may resort to feeding on each other. Either way, their numbers will die back to keep in the system in balance.

Ultimately, septic tank additives that are safe to use are unlikely to be effective, while additives that are effective are unlikely to be safe to use in your system. Rather just stay clear of them and let your system function naturally the way it was designed to. At the end of the day, there is no additive available that is capable of breaking down the layer of sludge that settles on the bottom of your tank, which will need to be pumped out at some point. To prevent system failure and to extend the life of your septic system, you would be better off saving the money you would have wasted on additives and rather spend it having your tank inspected and pumped out as and when required according to the recommended maintenance schedule.


Lee, Brad, Don Jones, Run Turco, Septic System Additives [PDF] HENV-13-W, Purdue University, Purdue Extension.

Septic Tank Additives. Small Flows Quarterly, Winter 2002, Vol. 3, No.1.

Washington State University, Don’t let your Dollars go Down the Drain! Septic Tank Additives [PDF] Washington State University Extension Clark County, WA

Luis Goncalves, ROWP, IN, PL

I fell into this amazing trade quite by accident, I have always loved being around heavy machinery and moving earth and in contrast love working with designing things.  This trade in the septic field has led me down a wonderful path of exploring all of my skills and passions while working hard at achieving success.

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