Grease Interceptor FAQs

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Grease Interceptor FAQs

Most local codes require volume-based grease interceptors to be pumped on a quarterly basis or by the 25% rule, whichever is more stringent. The wastewater in every grease interceptor is separated into (3) three distinct layers. All heavy solids will fall to the bottom and this layer is referred to as sludge while all lighter material such as grease will float to the top and this is referred to as the scum layer. The rest of the wastewater will remain in the middle and this layer is referred to as the clear zone.

When the layer of scum and sludge added together surpass 25% of the total liquid depth, it is time to have the interceptor pumped. This can only be determined when a competent contractor uses a sludge judge, dipstick, or similar tool to take these measurements. Most flow-based grease interceptors require daily maintenance and should be fully pumped at least monthly, however, local codes differ in requirements.

Unless the tank is being pumped by a contractor it should always be holding wastewater. The liquid level should be at the invert (bottom) of the outlet line. If the liquid level is below this point, there is a chance that the tank itself has been compromised and is actually leaking. This should be inspected by a qualified contractor. If the liquid level is above the invert of the outlet line, it is an indication of a problem with a downstream component.

Absolutely! Dishonest contractors are notorious for “skimming,” or only removing the scum layer from an interceptor. They do this so they can complete more jobs before being required to go to a disposal facility. A proper pumping of a grease trap/interceptor includes evacuating all contents from the tank.

Local codes will determine requirements. Some require volume-based interceptors to be powerwashed annually. However, the requirements are vague at best. When a pumping contractor pumps a volume-based interceptor they will only be able to evacuate the loose contents if they do not introduce a power-washing process. Grease, over time, will harden and stick to the surfaces of the interceptor.

The only way to remove this grease is to introduce additional cleaning methods, such as scraping the walls and powerwashing with a high-pressure water jet. We feel that a volume-based grease interceptor should be completely powerwashed at least annually and this should include a thorough water-jetting of the inlet and outlet drain lines to ensure that they are clean and free of anything that will result in a sewer stoppage.

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