If you are legally required to adhere to FOG ordinances your county or city likely has minimum grease trap cleaning requirements. In Atlanta, for example, restaurants with indoor grease traps are required to have them cleaned at least once every 14 days while outdoor grease traps must be cleaned at least once every 90 days.

In addition to these scheduling requirements businesses also must adhere to the 25 percent rule. That means the topmost layer of FOG in the grease trap plus the bottom layer of solids can’t total more than 25 percent of the grease trap depth.

Many businesses won’t reach that 25 percent threshold within the two weeks or three months between required cleanings, but some will. If you receive one of your yearly grease trap inspections when your FOG and solid depth is more than 25 percent of your grease trap depth you will likely be cited and be forced to schedule cleaning, then undergo grease trap reinspection.

Signs It’s Probably Time to Clean Your Grease Trap

If you haven’t been staying on top of your grease trap cleaning or you’re just not sure how frequently you should get them cleaned, you may want to keep an eye out for the following signs:

• Bad smells in your restaurant or outside
• Sudden clogs or backup in drains
• Water is draining more slowly than normal

Who Came up with the 25 Percent Rule?

Multiple regulators and FOG management organizations began adopting or encouraging cities and counties to adopt the 25 percent rule in the ‘90s. Multiple sources seem to suggest the original 25 percent rule was adopted in Honolulu. An official in their Department of Environmental Services, James Baginski, did some of his own testing to determine how full a grease trap could get before it started to let FOG escape. He found that most grease traps could safely and effectively maintain a 25 to 35 percent water to FOG ratio before it began losing effectiveness.

The regulators unsurprisingly settled on the conservative end of that range and went with a 25 percent requirement to reduce the chance for FOG to escape into Honolulu’s notoriously precarious sewer system.

The Plumbing and Drainage Institute (PDI) either did their own research or looked into and confirmed Baginski’s new best practice, as they began using the 25 percent threshold for grease trap performance reliability in their publications starting in the late ‘90s. 

How to Know When You’ve Hit 25 Percent

This is the harder part. Many restaurant and food service business owners don’t have their own FOG measuring tools. These measurement tools are essentially long tubes that need to be sunk into the grease trap till it hits the bottom. Then a lever or bar on the side of the tube is pulled to essentially trap a vertical sample of the grease trap’s contents. On the bottom of the sample will be the solids, in the middle will be the grey water and at the top will be the floating FOG. Since all the water and material in the tube isn’t being jostled it will remain separated in the same way it is separated in the grease trap.

You would then measure the depth of the solids at the bottom, the fog at the top and then divide the combined number by the total depth of the trap.

If a 48-inch deep grease trap has 6 inches of solid at the bottom and 3 inches of FOG floating at the top the calculation would be 9 divided by 48, which would give you 0.188 or approximately 19 percent. The grease trap wouldn’t be in violation range, but it should probably be cleaned soon.

The difficulty with testing yourself is one of the reasons Atlanta requires cleaning at the 14-day (for indoors) and 90-day (for outdoor) intervals. When your grease trap cleaning company comes out, they can measure your FOG levels and let you know where it’s at and whether you should consider scheduling cleanings at more frequent intervals.

Get Expert Grease Trap Cleaning in Georgia

If your food service business requires regular grease trap cleaning from certified, environmentally responsible grease trap cleaning and fryer oil recycling experts, Southern Green Industries can help. Our company is committed to making grease trap cleaning a smooth, worry-free process for food service businesses in Georgia.



Just call us at (404) 419-6887 to get started or to request a free quote on grease trap cleaning or fryer oil recycling.