This Is Why Your Septic Tank Needs To Be Pumped…


Table of Contents

Why do Septic Tanks Need to be Pumped?

Homeowners very often find septic tank maintenance a tad confusing, and are not sure whether their tank needs to be pumped or not. And those that are aware that their tank needs to be pumped out regularly may still not be sure why. To fully understand why septic tanks need to be pumped, one has to understand how a septic system functions.

A septic system typically consists of two major components: 1) the septic tank; and 2) the drain field. The septic tank serves as the core component where wastewater discharged from the toilet, bathtub, shower, kitchen and laundry is separated into three layers: scum (lighter particles that float to the surface); liquid (watery effluent); and sludge (heavier solids that settle on the bottom of the tank). Anaerobic bacteria that live in the septic tank break down the solids (sludge and scum), as well as any organic matter suspended in the liquid, into less complex organic compounds. However, they are only able to decompose a small percentage of the solids that remain behind in the tank.

The anaerobically treated wastewater flows out of the septic tank to the drain field where aerobic bacteria break it down further. The solids that are retained in the tank that are not broken down begin to accumulate and slowly fill up the tank — the lighter scum from the top down, and the heavier sludge from the bottom up.

septic system

A properly sized septic tank can typically store the solids that accumulate for up to three years — the length of time depends on the number of people living in the home, their water usage habits, and whether other solids such as kitty litter or food waste from a garbage grinder is disposed into the system. However, as the volume of accumulated solids increases, the amount of time that wastewater is retained in the tank before being released to the drain field decreases, and so does the efficiency of treatment.

As the space between the two layers gets smaller and smaller, the tank no longer has the capacity to store the solid particles. As a result, they start to flow out of the tank with the liquid effluent and will begin to clog up the pipes and soil in the drain field. If the soil absorption area becomes too clogged it will not be able to absorb wastewater effluent at the same rate that it enters the septic tank, which will either cause unsavoury effluent to bubble up to the surface of the soil or sewage to back up to the home.

why pump a septic tank

Some newer septic tanks have a filter fitted onto the exit pipe which captures solid particles and reduces the number of solids that flow to the drain field. While this filter may help protect the integrity of the drain field, it will result in a greater volume of solids remaining behind in the tank, which will need to be pumped out periodically.

When Does a Septic Tank Need to be Pumped?

More often than not you will receive some tell-tale signs that your septic tank needs to be pumped, including:

  • Pooling of water on the surface of your lawn
  • Lush green patches of lawn
  • Bad odours coming from the toilet, drain or septic tank
  • Sluggish flushing and/or draining
  • Sewage backing up to the house (worse case scenario)
sewage back up

To prevent your septic system from failing, it should be pumped out before the solids accumulate to the extent that they start to flow out of the tank with the effluent to the drain field. There are two ways to determine when your septic tank needs to be pumped. The first is simply to have it pumped out regularly say every two or three years.

The second is to open the inspection hatch of the tank once a year, and using a long section of PVC pipe or a pole, measure the depth of the sludge from the bottom of the tank, which will be visible as a dark stain on the pipe.


If the layer of sludge is greater than a third of the tank’s volume, it is time to have the tank pumped. To be on the safe side, it’s probably better just to have your tank pumped out routinely every two or three years, or more frequently if required.

One thing to note is that having a garburator will require more frequent septic tank pumping.  This is due to the small organic suspended solids that will not decompose in the tank very efficiently.

This increases the strength of the effluent (middle fluid zone in the septic tank) and can tax the drain field which can lead to a shorter lifespan.

why do I need to pump my septic tank

Having outside guests stay for extended periods should also require more frequent tank pumping, this is because there will be more solids accumulated in the sewerage system, more dishwashing which will lead to a higher strength effluent again. 

More showers and more laundry will also tax the system.  Therefore to give your onsite wastewater system a break, it will certainly be a good idea to have a septic tank pumping schedule to break up the heavy constant flows hitting the system.  It will at least give things a break for a few days before the tank fills up again.

If you decide to hold a barbeque, wedding party or other events where there will be a lot of people attending, it is a good idea to have your septic tank pumped just prior to the event.  It is always best to have preventative measures than costly repairs or messy malfunctions afterwards.  The massive volume of wastewater travelling through your system can easily overwhelm the drain field causing oversaturated conditions.  This can lead to pre-mature field malfunction or worse sewage back up into your home.

How Much  Wastewater is Produced by 20 Guests During a Party?

Let’s assume there would be up to 20 people visiting the home over a six-hour period if every guest uses the bathroom and at each use flushes a toilet twice, that will be approximately 40 x 4gals = 160 gallons, less than the septic tank can hold.

Assuming we have a typical 2-3 bedroom home with a septic tank of 1000 gallons or larger, and if we start our festivities with the tank nearly empty, we are sure to protect the drain field from oversaturating and potentially backing up during the event.

If the home’s septic system has been working well, then there should be no trouble with it handling the extra volumes for short intervals.  If the system is older and there are noticeable ailments such as slow flushing toilets then there could be issues when holding the party.

If you are unsure of whether or not to pump your tank, an inspection can be done and the scum and sludge layers can be measured, then keep records so that you have a consistent measure of maintenance and pumping.

Septic Tank Installation

Having a Home Business

More and more entrepreneurs are taking advantage of being at home, this is great in many ways but when it comes to your septic system caution is the word of the day.

business and septic systems

Having a hair salon, for example, can add volumes of harmful chemicals and bleaches into the system, this will affect the biology of the septic tank and the anaerobic bacteria that consume solids and organics.

Photography and taxidermy other examples where higher than normal volumes of chemicals are going to make their way through the septic system.  Running a daycare facility is also going to affect the system by adding more volume to the system.

Here are other reasons to pump your septic tank:

  • As already mentioned, but reiterating…Before the party: you can reduce the chances of a septic system backup as well as avoiding overloading the drain field if you have the septic tank pumped right before any anticipated heavy usage such as having many visitors or having a large party with many guests in your home.
  • Having a Sewage Back up and Responding:   when drain lines are backing into the home or building, having the tank pumped is a band-aid solution that will give temporary relief before the tank is full again.  This will give the homeowner a few days to find the system problem and have it fixed prior to the wastewater filling the tank again.
  • If the septic system is backing up because the drain line or tank baffles are totally blocked by solid waste then the septic tank will require pumping.  When sewage backs up into a home, it could also mean that the drain field is no longer accepting wastewater, this could mean replacement measures.
  • If the septic system drain lines, tank baffles or distribution box is clogged:  The empty tank will offer enough time to go through the system carefully to find the malfunction.


  • Real estate Sale:  during a real estate transaction, either the homeowner or the realtor arranges to have a septic tank pumped prior to an inspection.  Often a wastewater practitioner with an inspector classification will perform what’s called a dye test to see if there is a wastewater breakout anywhere down the system.  This type of conduct whether by the lack of knowledge on septic systems or by acting in the buyer’s favour is a fraudulent act in many jurisdictions.  This act will prevent a valid septic inspection from taking place, a septic tank can certainly be pumped after the inspection.
  • Septic systems that have been exposed to flooding conditions:   In recent events, we have seen homes near lakes and rivers become submerged in water.  This not only wreaks havoc inside the home but it causes an automatic septic system malfunction.  The drain field is immediately over saturated and will not accept any further water.  The only remediation is to allow the high water to subside, pump the septic tank and allow some time for the system to recuperate.  The tank then needs to be inspected for further water intrusion or backup of silt or mud. 
  • Filled cesspools or dry wells:  are often “repaired” by pumping and perhaps by other means such as agitating the cesspool bottom or sides. If a cesspool is found filled to within 6-12″ of the top of the unit it is at end of life and needs replacement. Pumping some cesspools risks dangerous cave-ins or collapse.

Although in Canada there is no definitive measure to a tank pumping schedule other than the suggested 3-5 year intervals.  I found these averages and placed them into a chart form from the Penn State College of Agriculture that may shed some insight:

When To Pump Out A Septic Tank

Here are a Septic Tank size requirements for British Columbia based on the homes daily flow:

Daily Flows From Homes:

Daily Design Flow of home

How To Find Your Septic Tank

The first step in finding your septic tank is to find your records. All recent septic system approvals paperwork should contain an as-built drawing that will help you find the system.

If you don’t have a copy of the paperwork, a copy may be available from your local regulatory agency.

If you don’t have an as-built drawing, start by trying to locate the septic tank. Go to your basement and look where your sewer pipe leaves the foundation.

how to find your septic tank

Try to find this same spot on the outside of the house. As a good starting point, measure out 1.5 metres (5 feet) from the house.

Using a blunt metal probe, try to identify the corners of the tank. It may take some time based on how deep the tank is buried.

Be sure to exercise proper caution — if gas pipes or utility lines lie close by, be sure to call before you dig. If you can’t find the septic tank using these methods, contact your licensed sewage pumper or onsite sewage system professional for help.


The septic tank is a key component of a wastewater treatment system. Its main function is to separate and remove solids from the wastewater effluent before it flows to the drain field and to partially digest a percentage of these solids and store those that remain. These solids need to be removed regularly to prevent them from accumulating to the extent that they enter and clog the soil absorption area in the drain field, where they can cause the system to fail.

If you are a nonresidential system owner, you should determine how often to pump based on prior accumulation and pumping records. Often you can look at pumping intervals to gauge your pumping schedule (i.e., previously did you wait too long before having your tank pumped and it was filled to capacity, or could you have waited a little longer to pump?).

An amazing number of system owners believe that if they haven’t had any problems with their systems, they don’t need to pump out their tanks. Unfortunately, this is a serious and sometimes costly misconception.

When hiring a pumper, be sure the governing association (ASSTTBC) has licensed them, and always make sure you get a paid receipt from the pumper that spells out the details of the transaction (how many gallons were pumped out of the tank, the date, the charges, and any other pertinent results). Retain this receipt for your records. The pumper sends a copy of this report to the local Board of Health.

We’re happy to help with any questions so please don’t hesitate to connect with us:

Luis Goncalves, ROWP, IN, PL


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.

Table of Contents

More Posts