A Canadian restaurant owner’s guide to grease traps

Category: Restaurant
20 Jan 2023

In a home scenario, Fats, oils, and grease (FOG) that is sent down the drain will float to form the scum layer in a septic tank. Eventually, it will be pumped out during the septic tank cleaning. FOG therefore seldom causes problems for homes. But FOG can be a huge problem for restaurant owners. Restaurants produce too much FOG which can easily cool down en route to the septic or sewer system. This would result in pipe clogging. Grease traps are, therefore, used to prevent this from happening.

What is a grease trap?

A grease trap also referred to as a grease interceptor, is a plumbing device that catches and collects FOG from wastewater. Some grease traps also have components for collecting food particles and other suspended solids. Grease interceptors are mainly used in restaurants because they produce quite a lot of FOG. The following are the main types of grease traps.

Hydromechanical grease traps

Hydromechanical grease traps can be thermoplastic (made from Polypropylene, High-Density Polyethylene (HDPE), or Low-Density Polyethylene (LDPE)), or they could also be made from prefabricated steel. These grease interceptors separate and retain FOG from wastewater via internal baffling, air entrainment as well as hydraulic flow techniques.

Passive grease traps

Passive grease interceptors have a series of compartments through which wastewater from the kitchen passes. They cool down the wastewater thereby allowing the FOG therein to float to the top while other food debris settles at the bottom. Passive grease traps must, therefore, hold the water long enough to allow the FOG to float. These grease traps are efficient, allowing 90% of FOG to be collected out of the water.

Automatic Grease Removal Unit (AGRU)

AGRU grease traps rely on mechanical and electrical components to remove FOG from the wastewater. AGRU grease traps are very small but quite efficient. An AGRU unit can eliminate up to 99% of the FOG in your wastewater. Some AGRU units also come with a collection device for collecting food particles and other suspended solids.

What does a grease trap look like?

A grease interceptor looks like a miniature septic tank. A typical grease trap will have the following components:

  1. Inlet – this is where wastewater from the kitchen and other fixtures flows into the grease trap
  2. Flow regulatory device – It is placed next to the inlet and its purpose is to regulate the flow of wastewater into the grease trap. Each grease trap has a rated capacity and this device ensures that the recommended capacity is maintained.
  3. Air intake vent – this vent allows air to enter the open space of the trap. This helps to avoid siphonage or back-pressure.
  4. (Removable) baffles – baffles help in retaining the grease towards the upstream end of the trap. This is because FOG floats and will therefore not go below the baffles. This helps to prevent the FOG from escaping the trap and moving through the plumbing where it can cause blockages.
  5. Solids accumulation – any solid that does not float will settle down to the bottom of the grease interceptor. These solids will eventually be removed during the routine cleaning of the system.
  6. FOG accumulation – Fats, Oils, and Grease floats to the top and then accumulates behind the baffles. The accumulated FOG will be removed during the routine cleaning of the grease trap.
  7. Air Relief – the air relief component helps to ensure there is proper air circulation in the grease trap.
  8. Sample point – a sample point is used at the outlet of the grease trap to sample the quality of the wastewater that comes out.
  9. Cleanout – the cleanout is placed near the outlet and it provides access into the pipe in case one needs to remove anything that is causing blockages.
  10. Outlet – wastewater that has been separated from FOG leaves the grease trap through the outlet.

Are grease traps mandatory?

Grease traps are mandatory for businesses that have commercial kitchens. A business that has a commercial kitchen is any establishment that heats, cooks, processes or prepares food onsite. Grease traps must, therefore, be installed in the following facilities:

  • Foodservice businesses (e.g. coffee shops, restaurants, banquet halls, etc.)
  • Mobile food vendors
  • Child care centers

Why do restaurants need grease traps?

Restaurants are required to install grease traps. When grease traps are not used for these establishments, the warm fats, oils, and greases make it into the plumbing pipes where they cool down and stick to the pipe surfaces. This accumulation of FOG in the pipes eventually results in the clogging of the pipes and this creates lots of other problems including:

  • Sewage backups into your business, local rivers or other neighboring properties
  • An increased vermin contact with the disease-causing microbes which could expose all your staff and clients to harmful diseases
  • Cleaning and repair of the blocked systems will cost you a lot of money
  • Your facility might be temporarily or even permanently closed down by public health officials


Grease Trap Installation

How much do grease traps cost?

The average cost of installing a grease trap is C$6,000 but the figure can be as little as C$300 or as much as C$13,000 depending on a number of variables. Some of the factors that affect the pricing are the size of the grease interceptor, the local hourly rates, the cost of the materials used, the cost of preparing your surface, local permits that might be required, and the general fees charged by your contractor.

What size grease trap do I need?

The size of the grease trap your restaurant needs is determined by the rate of wastewater flow which is measured in gallons per minute (GPM). But on a bare minimum, the grease trap should be large enough to allow for the retention of FOG until it is properly cleaned and disposed of. The capacity of your grease interceptor is given in pounds and it is determined by multiplying the GPM rate by two. For instance, if your GPM is 15, you will need a grease interceptor that has a 30 pound rated capacity. Use the following formulas to compute your sink’s GPM:

  • Start by getting the volume of your sink (length x width x depth). That should give your sinks capacity in cubic inches.
  • Divide the figure you got in the step above by 231 in order to get the GPM value
  • Adjust for displacement by multiplying your GPM value by 0.75 and then by two.
  • The figure you get is the flow rate capacity of the grease trap that you should install.

Just to be on the safe side, you can always go for a size higher than the one that is recommended for your GPM rate.

How to build a grease interceptor

You can build a DIY grease trap, if there are no specific regulations prohibiting it in your area, by converting a large plastic water barrel into the grease trap. Here is a step by step procedure of how to do this.

  • Get a 55-gallon water barrel and draw a straight line all around it. This line should be 6 inches from the top.
  • Using a hand saw, cut off the top of the barrel by carefully following the line you drew in step one above. Set the top side you have cut off aside because you will use it as the lid.
  • Measure the outside diameter of the outlet pipe from the sink at the point where you are going to install your grease trap.
  • Draw circles on two opposite ends of your barrel. The circles should be the exact same diameter as the measurements you took in the previous step and they should be 6 inches from the open rim.
  • Cut around the circles with a razor pen so that the incisions made leave you with two evenly sized circles that are slightly bigger than the outlet pipe from the sink
  • Measure the width and height of the barrel (inside measurements). Cut a plastic sheet that is exactly the same width as the inside barrel width and 6 inches shy of the height of the barrel.
  • Insert the plastic sheet such that it hangs right in the center of the space between your outtake and intake holes and the top edge is flush with the rim of the barrel.
  • Use a plumbing sealant to seal the inside of your barrel
  • Place the barrel at the install point and as close to the sink as possible and then reroute the pipe from the sink to the intake side (west side) and the soil line from the outtake side (east side). Insert the pipes into the respective holes and then seal off the open spaces with plumbing sealant
  • Install an elbow joint pipe at the end of the outtake pipe in the barrel and make sure the opening of the joint is facing downwards. Add a 6-inch long pipe to the open side of the joint and then place the top on the barrel to close it.

Where is a grease interceptor usually installed?

A grease trap should be installed in an easy-to-reach area because it will need to be cleaned regularly. The most practical location for installing the grease interceptor is under the sink. However, it is also possible to install it outside. If you have only one sink, the internal grease interceptor will be ideal but restaurants that have more than one sink are better off with an external grease trap because all the drainage pipes can be fed into one outlet which can then be connected to a single grease interceptor.

Grease Trap Maintenance

How often do you need to clean a grease interceptor?

How often you clean your grease trap will be determined by how much FOG you produce. The FOG layer in the grease interceptor should not be allowed to go beyond 2 inches in thickness so you should clean your interceptor as soon as it gets to 2 inches.  You can measure the FOG levels in your grease trap using the following steps:

  • Locate and open the lid of the grease interceptor
  • Using a turkey baster, pry and break through the FOG layer at the top of the interceptor. If the FOG layer is thick and hard to break through, clean your interceptor immediately. Otherwise not, proceed to the next step below.
  • Take a sample of the liquid using your baster. Start by taking a sample 1 inch into the liquid. If this sample contains FOG, insert your barter 2 inches then and observe for the presence of FOG and then insert it 2.5 inches deep. By the third try, you should have little or no FOG. If this is not the case, it is time to clean your grease interceptor.
  • Repeat this test several times and it will give you a good estimate of the duration of time after which your grease trap will typically be ready for cleaning.

How do you clean a grease trap?

You can either hire a company that specializes in cleaning grease traps or you can do it for yourself. If you chose to do it for yourself, make sure to adhere to all safety requirements like the use of personal safety equipment. Also, remember to keep a log of the times you have cleaned your grease interceptor in case you are called upon by the authorities to produce proof of regular cleaning.  Here are the steps to follow when cleaning the grease trap:

  • Prepare some empty containers for transferring the grease and any solids that you will find when cleaning the trap
  • Remove the lid of the grease interceptor
  • Scrape of the FOG layer
  • Remove the water and then remove any solids that might have settled a the bottom of the grease trap
  • Scrape any residual FOG on the lid, baffles, and sides of the grease trap
  • Check the inlet and outlet to make sure they are clear and clean
  • Reinstall the seals and replace any that are cracked or brittle

Where to dump grease waste

The grease interceptor waste should be cleaned and dumped at licensed disposal facilities. If you have a small establishment that uses a small grease interceptor, you can clean the interceptor yourself and bag the grease interceptor waste in a watertight bag which you can then dispose of with other kitchen waste. For larger establishments, you may want to use a licensed contractor that specializes in grease interceptor waste cleaning and collection.

How much does it cost to clean a grease interceptor?

The cost of cleaning a grease trap can be as little as C$100 or as much as C$1,500 depending on how big your trap is and how much FOG you collect. For instance, if you have a tiny indoor grease trap of around 20-30 gallons, you will probably need to pump it once or twice a month and it will cost you approximately C$100. The cleaner will probably need 20-30 minutes to complete the job. Busy establishments need large grease traps because they produce a lot of FOG. A 5,000-gallon grease trap would take a cleaner approximately 2-4 hours to clean it and it will cost you approximately C$1,500. These two price points represent the two extremes and most restaurant owners will fit somewhere between the two. Most cleaning companies will charge less if you commit to a regular cleaning schedule with them. This is because the first is usually the hardest and most expensive but if you stick to a regular cleaning schedule, the process will be more efficient and less laborious.

What does a grease trap smell like?

Grease traps often emit an odor that is comparable to that of rotten eggs. As your trap intercepts the FOG from your wastewater, it will also inevitably hold some food particles which will then settle at the bottom of the grease interceptor. Naturally occurring microorganisms will start breaking down this organic waste and this process results in the emission of hydrogen sulfide. Hydrogen sulfide has a rotten-egg smell and this is why the traps smell that way.

How do I stop my grease interceptor from smelling?

The most efficient way to deal with grease trap odors is to clean it. Since these odors are caused by the digestion of organic waste, removing organic waste will solve the problem. If the odors persist even after cleaning your grease interceptor, then the odor might be coming from somewhere else.

  • If the odor only occurs when the kitchen is in use or after flushing the toilet, you probably have a faulty vent, a wobbly toilet or a problematic wax seal. Get in touch with a plumber to look into this.
  • If the odor is outside, you probably have a problem with the city plumbing or your onsite waste management system. If you are a septic system owner, the odor might point to a blocked drain field and adding biological additives from Bio-Sol should fix the problem. Adding biological additives to the grease trap will also make the emptying of the grease trap less frequent which ultimately saves you your hard-earned money.

As a precaution, always inspect your grease trap to ensure it does not have any cracks and the lid is tightly shut. Any damaged parts should be repaired or replaced immediately. If you do this and clean out the trap regularly, you will eliminate the nasty odors from your restaurant.

Are grease trap fumes toxic?

The main fumes found in grease interceptors are sulfuric gases and hydrogen sulfide.  Hydrogen sulfide is a toxic gas and according to the CDC, This gas is easily absorbed through the lungs and too much exposure to it can lead to various problems. For instance, prolonged exposure can cause painful dermatitis and burning eyes. Direct contact with it can also result in frostbite. Other sulfuric gases are also quite toxic. The breathing of sulfuric gases causes irritation in the nose, airways, and throat. This leads to wheezing, coughing, and shortness of breath. These gases can, therefore, be extremely dangerous for any asthmatic condition. As long as the trap is well maintained and functioning properly, these gases should remain trapped therein and therefore pose no risk.

Does a grease trap need to be vented?

Venting is a legal requirement for grease traps. The vents will limit the probability of pressure and gas building up within the trap. Accumulation of gases in the trap is not safe especially since the trap gases are flammable and explosive. The vent will also help to restrict the flow of sump which could cause backups.


A grease trap is not needed for your house. A domestic household doesn’t produce too much grease and the FOG that goes down your drain will float in the septic tank to form the scum layer. This scum layer actually helps to create a conducive environment for anaerobic bacteria because it acts as a seal on top of the wastewater. The Scum will eventually be pumped out with the other wastewater during the regular cleaning of your septic tank. However, grease traps are a must-have for any establishment that has a commercial kitchen, e.g. a restaurant. Such establishments produce so much grease that if grease traps are not used, the FOG would cause blockages and lots of other plumbing problems. The grease trap must be cleaned and inspected regularly to ensure it is in optimal working condition.

About the author


CEO at Bio-Sol

Our goal is not only to offer you the best products on the market but also to educate and empower you with the insights you need for successful wastewater treatment.


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