Grease traps and grease interceptors capture fats, oils, grease, and some solids before kitchen wastewater reaches the sanitary sewer. Pump-out planning is controlled by the installed product, actual accumulation, local FOG ordinance or permit terms, sewer-authority inspection method, service records, and manufacturer instructions.
This guide explains common threshold concepts, local FOG accumulation screens, record keeping, and source boundaries. It is not a permit, inspection result, plumbing design, product-listing decision, pretreatment compliance determination, or sewer-authority approval.
Threshold Screens and Measurement
Many local programs use a grease-plus-solids accumulation threshold, often expressed as a percentage of the liquid depth or effective capacity. A 25% screen is common enough to be useful for planning, but the actual threshold, maximum interval, measurement method, and corrective action are local-program questions.
A field log normally needs consistent measurements of floating grease, water depth, and settled solids before service:
- Floating grease layer: Record the depth from the surface to the grease/water interface using the method accepted by the local program.
- Water depth: Record the total liquid depth or effective capacity basis specified for the unit.
- Settled solids: Record the solids layer using the local method, hauler method, or inspection procedure.
Local screen example: (Grease Layer + Solids Layer) / Water Depth
Example: A trap with 24 inches of liquid depth and 7 combined inches of grease and solids screens at about 29%. Whether that requires immediate service, corrective action, or a record update depends on the ordinance, permit, inspector, and service agreement.
Grease Trap Pumping Schedule Calculator
Calculate grease trap pumping frequency based on trap size, flow rate, and grease accumulation. Meets the 25% rule for FOG compliance.
FOG Accumulation by Kitchen Type
FOG accumulation can change quickly with menu, fryer use, dishwashing practice, solids loading, flow rate, and seasonal volume. Per-meal estimates can help build an initial screen, but they should be treated as local source-gap rows until measured against the actual trap or interceptor.
- High-oil or frying-heavy menus: usually need closer measurement and shorter review cycles.
- Moderate general cooking: still needs field logs because pot washing, dishwashing, and prep practices dominate.
- Bakery, deli, or low-cook operations: may produce lower FOG, but butter, icing, wash-down, and solids can change the result.
Record grease and solids depths at consistent points in the service cycle. The interval should be based on actual accumulation, local maximum interval, product condition, and sewer-authority review rather than a generic meal category.
Sizing and Product Review
Pumping frequency does not prove that the grease-control equipment is correctly sized, listed, installed, accessible, or approved for the connected fixtures. Sizing and product selection depend on the adopted code edition, local amendments, PDI or ASME context where applicable, manufacturer data, fixture routing, flow-control fittings, dishwasher and disposer rules, and AHJ or sewer-authority interpretation.
A very short measured service interval can be a reason to review the product, connected fixtures, kitchen practices, and service plan. It is not by itself a code determination. A qualified plumber, manufacturer, and sewer authority should review whether the unit, access, flow control, venting, and maintenance procedure fit the actual operation.
Records and Best Practices
Local programs may require pump-out manifests, hauler information, disposal records, inspection logs, depth measurements, corrective-action records, and record retention for a defined period. Do not assume the record format or retention period; verify it with the local sewer authority or permit.
Best practices usually focus on keeping FOG and solids out of the drain before they reach the trap:
- Dry wipe and scrape: Remove grease and food from pans and dishes before washing.
- Proper oil disposal: Put used cooking oil in designated containers, not sinks or floor drains.
- Solids control: Use strainers where allowed and empty them on the required schedule.
- Fixture routing review: Verify dishwasher, disposer, floor-drain, and pre-rinse connections with the local authority and manufacturer.
- Additives: Verify enzyme or bacterial products with the local program before using them, especially if they can emulsify grease downstream.