Apply the '25% rule' to determine when a grease interceptor requires pump-out

Steps

1. Confirm the local FOG ordinance's exact wording, since jurisdictions vary between measuring combined floating-grease-plus-settled-solids depth against total liquid depth versus other formulations
2. Take a core sample of the interceptor's full liquid column using a device such as a sludge-judge/dip-stick style sampler rather than only visually inspecting the surface
3. Measure the combined depth of the floating FOG layer and the settled solids layer, then express that combined depth as a percentage of total liquid depth in the compartment
4. Trigger pump-out and cleaning once the combined accumulation reaches approximately 25% of liquid depth, or at the jurisdiction's mandated minimum frequency (e.g., a fixed quarterly or monthly schedule), whichever comes first
5. Document the measurement and service date on the facility's maintenance log/manifest to demonstrate compliance during inspections
6. Note the historical origin of the rule (commonly attributed to a Honolulu regulatory analysis in the late 1990s finding tested hydromechanical interceptors' grease storage capacity fell in a 25-35% range of total volume) purely as background — do not treat the origin story as itself a compliance standard