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Frequently Asked Questions

Q: When should I empty my septic tank?


A: Quebec regulations provide for two methods for emptying the sludge and scum accumulated in septic tanks. 


1. At regular intervals: 

  • At least once every two years for septic tanks used year round;
  • At least once every four years for septic tanks used seasonally (180 days or less per year).

2. According to the measurement of sludge and scum, if a municipality has adopted a by-law providing for the emptying of septic tanks on its territory. In this case, septic tanks must be inspected once per year and be drained when the thickness of the scum layer or the sludge layer reaches one of the maximums specified in the by-laws.

Q: What should be done before emptying?

A: Remove the lid from the end of the tank, where the baffles are located.

Q: What actions and habits should I take to promote the proper functioning of my water treatment system? 

A: Several habits make it possible to promote the proper functioning of a device for treating wastewater. For example:

  • Make sure you know the location of the components of your water treatment device.
  • Avoid driving over the components of the treatment device as this may cause breakage of piping, tanks or other components of the treatment system. Driving on the area could also compact the soil and result in poor sewage disposal and treatment.
  • Do not plant trees or shrubs near pipes because their roots could clog them. Maintain a free zone of at least 3 meters.
  • Have your septic tank drained by a professional when required.
  • Only channel sewage and household water to your treatment system (do not connect foundation or roof drains).
  • Use household cleaning chemicals in a moderation. Do not pour paint, gasoline, pesticides, oil, antifreeze, or other chemicals into your sinks or toilets. These products are toxic to the bacterial flora of your water treatment system.
  • Avoid throwing dental floss, feminine hygiene products, condoms, diapers, cigarette butts, cotton swabs, coffee grounds, cat litter, paper towels or other household items that may cause breakage of the treatment device.
  • Use water responsibly and quickly repair leaky faucets and toilets since the greater the water consumption, the heavier the load on the treatment system, increasing the risk of malfunction.
  • Avoid the use of additives. Additives that are sometimes suggested to add to the contents of septic tanks are not necessary. Some are even discouraged because they can interfere with the proper functioning of the septic tank and the leaching field.
  • Avoid throwing fats down the sink (cooking oils, greasy broths and others) because they build up in the septic tank.
  • Avoid waste disposers (garburators), as these create heavy loads and high accumulation of sludge in the septic tank.
  • Follow the recommendations in the manufacturer's guide.

Q: What about phosphates?

A: Reduce or, better yet, completely eliminate the use of cleaning products, detergents and soaps containing phosphates. Phosphorus does not decompose in the septic tank and when it flows into a nearby body of water, it causes rapid growth of blue algae (cyanobacteria) affecting water quality and aquatic life in general.

Q: What is done with the contents of the tank after pumping?

A: The waste is transported to a sewage treatment plant.

Q: What are the signs of an overfull tank, blockage or problem with the purification field?

A: There are several signs that indicate a problem with a septic system, including the following:


  • Toilets or sinks are slow to drain.
  • Odours coming out of your plumbing.
  • Reflux of water in washbasins, baths or showers after flushing the toilet or after washing.
  • Green stripes or spotted lawn in the perimeter of the leaching field.

Q: What is the smell that comes from the tank when the lid is removed?

A: What you are smelling is methane, a gas produced by the decomposition of organic matter.

Q: Can a water softener damage a septic system?

A: Concerns have been raised about this – such as the destruction septic tanks bacteria by salt, flooding of tanks by the backwashing process, and reduction in the capacity of the leaching field to absorb water. Recent studies are inconclusive on the subject.


It was found, however, that the salt did not adversely affect the bacteria or soil in the leaching field. That said, the volume of water resulting from backwashing can reach between 55 and 400 liters per week, equivalent to one or two standard baths filled with water. Not reloading the softener more than once a week should reduce the amount of backwash entering the septic system.


Sources and references: Canada Mortgage and Housing Corporation

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