Percentage of grease and solids that triggers mandatory commercial grease trap pumping?

Commercial grease traps require mandatory pumping when combined fats, oils, grease, and settled solids reach 25 percent of the unit's total liquid depth, standard under the EPA and municipal sewer ordinances nationwide.

Commercial kitchens, food service facilities, and plumbing contractors face strict municipal discharge limits to prevent fats, oils, and grease from clogging public sewer mains. Exceeding interceptor capacity causes direct grease pass-through into municipal lines, resulting in utility surcharges, plumbing backflow hazards, and emergency line blockages.

If you only do one thing: Measure your trap monthly with a clear core sampler and schedule pump-outs whenever the combined top grease cap and bottom sludge layer equal one-quarter of the total water column.

• The 25 Percent Rule: Municipal sewer authorities and the Uniform Plumbing Code mandate that hydromechanical and gravity grease interceptors undergo complete evacuation once grease and settled solids exceed 25% of total liquid capacity.
• Core sampling measurement: Plumbing technicians determine compliance by lowering a calibrated clear sampling tube to the tank base, measuring the top grease cap thickness plus bottom food sediment against total liquid depth.
• Hydraulic retention threshold: Operating past the 25% capacity threshold degrades hydraulic retention time, preventing buoyant separation and washing liquid fats straight into downstream building lines.
• Service frequency windows: High-volume commercial kitchens generally hit the 25% accumulation limit every 30 to 90 days, while exterior gravity interceptors sized from 750 to 1,500 gallons standardly require evacuation at least once every 90 days.
• Compliance manifest logging: Health inspectors and local sewer districts mandate on-site logbooks detailing pump-out dates, total gallon volume removed, disposal facility manifests, and licensed contractor credentials retained for 3 years.

• Watch out for: Chemical or biological emulsifiers, degreasers, and scalding water flushes designed to dissolve grease, which violate municipal pretreatment bylaws by re-solidifying fats downstream in public mains.
• Watch out for: Partial skim servicing that only removes floating grease while leaving heavy food sludge at the tank floor, which cuts liquid retention capacity by up to 50%.
• Watch out for: Undersized grease interceptors that reach the 25% solids limit within 10 to 14 days, signaling the need for an engineered capacity upgrade or supplemental fixture strainers.

Gauge your interceptor liquid profile with a core sampler this week; if combined solids exceed 25% of total depth, call 866-399-2885 to book commercial drain cleaning and plumbing line maintenance.