Grease Trap Services Seattle

What to Consider When Sizing Your Grease Trap

What to Consider When Sizing Your Grease Trap

Keeping greasy stuff away from plumbing systems and sewers is one of the waste management responsibilities of restaurant owners. Grease from your kitchen can’t get into waste water treatment facilities. Once grease gets into the environment, it’s difficult to get rid of it. But it’s not enough to have a grease trap. You have to choose an interceptor of the appropriate size for your sink. Grease trap sizing in Seattle isn’t an option for restaurateurs but a necessity.  

Anatomy of a Grease Trap

A typical grease trap in a typical restaurant is usually made for sinks, where grease from food preparation comes from. The inlet side has a flow restrictor that slows down the passage of waste water and diverts it through the baffling to allow lighter stuff in the effluent to rise and accumulate inside the trap. 

Sizing Your Grease Trap

The design of grease traps varies from restaurant to restaurant and is usually governed by local plumbing codes. Restaurant owners are expected to follow the guidelines set by the Plumbing and Drainage Institute (PDI). The guidelines state sizing requirements for interceptors.  

The size of commercial grease traps depends largely on the flow rate of washing sinks in gallons per minute (GPM). In other words, trap’s capacity will have to depend on how much waste water comes out of your sink. The larger and busier your kitchen is, the more effluent it produces and so the bigger the trap needs to be.  

Now, double the flow rate number, and you get the trap’s capacity in pounds. For example, your sink’s flow rate is 10 GPM. That means you need a trap whose capacity is 20 pounds. Keep in mind that this is a general formula. The actual capacity of your grease trap may still depend on a few other factors. Nonetheless, plumbers and regulatory agencies generally follow this formula. You can always ask our grease trap technicians in Seattle to help you with proper grease trap sizing.  

But how do I determine the flow rate of my sink?

Try asking your sink manufacturer regarding the accurate capacity of your sink. If obtaining this information from them is out of the question, you can still get the precise capacity of your sink by measuring the length, width, and depth of your sink in inches. Multiply the three numbers, and you get the capacity in cubic inches. You can now use that figure to determine the flow rate of your sink. Divide the number of compartments by 231 — that gives you the flow rate in gallons per minute.

Once you get the flow rate, you can now calculate the capacity of your trap. Adjust that GPM number by multiplying it by 0.75, the usable capacity of your sink. Then, multiply the product by 2. Finally, you now have the flow rate capacity in pounds.

If you have multiple sinks draining into one grease trap, calculate the flow rate for each sink using the formula above. Keep the flow rate of the largest sink the same, but halve the flow rate of the second largest, and get just a quarter of the flow rates of the rest. Add all the adjusted numbers to get the recommended flow rate capacity of the grease trap.  

What if I have a dish machine?

Dish machines should have their own grease traps. You should ensure that your dish machine has a suitably sized grease trap. The principle is basically the same. The larger your dish machine, the bigger its trap needs to be. The following table offers you an idea. 

Dish Machine Tank Capacity in Gallons 

Grease Trap Capacity in Pounds 

10 – 15 


20 – 30 


30 – 50 


50 – 70 


70 – 100 



Seattle grease trap sizing can be challenging in many instances. If you’re worried about precision in your estimates, or if you don’t know the exact capacity of your dish machine or sink, we can do the calculations for you. We have specialists who can visit your establishment and provide accurate estimates. Call Seattle Grease Trap Services at 206-880-7424.  

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