How a Septic System Works

A septic system consists either of a septic tank and a weeping bed or a septic tank and a tertiary system, which may or may not have a weeping bed.

Anything which goes down your drain will exit the house through an underground pipe and enter the septic tank. The tank itself consists normally of two chambers. The first chamber allows the heavier solids to settle to the bottom of the tank, the second chamber allows for finer solids to settle. A layer of scum is common in many septic tanks and generally consists of toilet paper, oils, grease, fats and soap.

A septic tank is always “full” in that the level should remain constant. The level should be just below the outlet pipe (the one leading from the tank to the weeping bed or tertiary system). Every time waste water enters the septic tank, the same amount will exit it as a result of displacement.

Organic materials which are in the tank will be broken down by anaerobic bacteria, and a certain degree of treatment is therefore achieved.

Modern tanks (generally since January 2007) will contain an effluent filter. This is located at the outlet pipe and prevents solids from entering and clogging the weeping bed or tertiary system. It also allows for more treatment of solids to occur by the bacteria in the tank.

A video from the Ontario Ministry of Agriculture, Food and Rural Affairs

how your septic system works.

What you should do

  • Familiarize yourself with the location of
    your system
  • Test your well water at least 3 times per year (spring, summer & fall)
  • If you have an effluent filter, clean it at least once a year (although spring and fall would
    be best). If you don’t have one, consider adding one.
  • Conserve water to minimize the amount of wastewater going through your system
  • Repair leaky plumbing fixtures
  • Install low-flush toilets
  • Take shorter showers or install water savings fixtures
  • Use eco options on your dishwasher & washing machine
  • Have your septic tank emptied regularly by a licensed plumbing company


The frequency depends on the number of residents. An approximate guideline is

  • every 4 years for 3 people
  • every 3 years for 4 people
  • every 2 years for 5 people
  • yearly if more than 5 people

What you shouldn’t do

  • Do not pour oil, grease, food waste, hazardous chemicals or paint down your drain
  • Don’t do all your laundry in one day, space out the use of dishwashers, showers and washing machines so the weeping bed has time to absorb the water
  • Do not drive or park on your septic tank or weeping bed
  • Do not plant shrubs or trees on or near your septic tank or weeping bed
  • Don’t flush sanitary pads, tampons, cigarette buds, condoms, wet wipes (even “flushable” ones), etc.


Flush only the 3 Ps: pee, poo, and (toilet) paper!

Septic System Approval Process



(1) The minimum working capacity of a septic tank shall be the greater of 3 600 L and,

(a) in residential occupancies, twice the daily design sanitary sewage flow, or

(b) in non-residential occupancies, three times the daily design sanitary sewage flow.


(2) Every septic tank shall be constructed in such a manner that any sanitary sewage flowing through the tank will pass through at least 2 compartments.


(3) The working capacity of the compartments required in Sentence (2) shall be sized such that,

(a) the first compartment is at least 1.3 times the daily design sanitary sewage flow but in no case less than 2 400 L, and

(b) each subsequent compartment shall be at least 50% of the first compartment.


(4) Where multiple tanks are to be used to meet the requirements of Sentences (2) and (3), the tanks shall be connected in series such that,

(a) the first tank in the series shall have at least a capacity as calculated in Clause (3)(a), however at no time shall a tank having a working capacity of less than 3 600 L be used,

(b) all additional tanks after the first tank, excluding pump or dosing tanks shall have at least a working capacity equal to the volume required by Clause (3)(b),

(c) the pipe between the outlet of one tank and the inlet of the next tank in the series shall have a minimum slope of 2 per cent,

(d) there shall be no partitions in the tank except where a partition is required to maintain the structural integrity of the tank, in which case openings within the partition shall be provided to allow the free movement of sanitary sewage throughout the tank, and

(e) all piping between tanks shall be continuous and shall be connected to the tank through the use of flexible water tight seals that will permit differential movement between the tanks.


(5) Partitions separating the septic tank into compartments shall extend at least 150 mm above the liquid level at the outlet, and there shall be one or more openings through or above the partition.


(6) The openings required between compartments referred to in Sentence (2) shall have a total cross-sectional area of at least three times the area of the inlet pipe and be located between the top and a level 150 mm above the liquid level at the outlet to provide for the free flow of air between compartments.


(7) Sanitary sewage shall pass from one compartment to another of the septic tank as follows:

(a) by means of a device similar to that described in CSA B66, “Design, Material, and Manufacturing Requirements for Prefabricated Septic Tanks and Sewage Holding Tanks” for outlet devices, or

(b) through two or more openings through the partition located in a horizontal line, and evenly spaced across the width of the partition, centred at approximately 40% of the liquid depth below the surface of the liquid, and having a total area of between three and five times that of the cross-sectional area of the inlet pipe.


(8) septic tank shall be of such design and construction as will permit the collection and holding of sanitary sewage in it to a depth of not less than 1 000 mm, except that a depth of not less than 900 mm is permitted where the excavation is in rock, or to avoid rupture or displacement of the tank due to ground water pressure.


(9) Except as provided in Sentences (10) and (11), every septic tank shall be installed in such a manner that the access openings are located not more than 300 mm below the ground surface.


(10) Where the top of the septic tank is located more than 300 mm below the ground surface, it shall be equipped with risers that extend from the access opening of the septic tank to within 300 mm of the ground surface.


(11) Where risers are used they shall conform to the requirements of CSA B66, “Design, Material, and Manufacturing Requirements for Prefabricated Septic Tanks and Sewage Holding Tanks”, and shall have adequate access openings to allow for regular maintenance of the septic tank.

Septic Inspections

How To Perform a Good Inspection

How can you accurately inspect a septic system?

Lets first look at what a septic system has to be doing correctly to be considered a properly functioning system:

Bacteria within the tank and bed must convert complex organic matter such as toilet paper, fecal matter, ammonia, fats, oils, greases, etc into basic molecules such as water, nitrogen, and co2. If the bacteria are not breaking down the complex molecules then the system will fail because untreated sewage will simply pile up and prevent all sewage from entering the soil. The septic tank is capable of treating up to 60% of the sewage if it is working properly. The remaining 40% must be treated within the treatment/disposal bed area.

The efficiency of a septic system can easily be assessed by looking at the bacterial health within the tank AND in the treatment/disposal bed.

A common practice within the septic industry is to only look at the septic tank to identify how well the system is working. Unfortunately though, the tank is rarely the part of the system that fails and needs to be replaced. A treatment/disposal bed failure is what causes the septic tank to back up and “fail”.

By locating and uncovering a very small section of the bed we can identify where on the scale of “failure” the system is. If the system is only partially failed then it may be possible that the system can be revived with proper maintenance. If the failure is more advanced then other actions can be recommended to reverse the failure. It is also necessary to look for root and dirt damage within the septic bed with a sewer camera whenever possible.

Good trench

Partially fixed

completely fixed