Grease Trap Requirements
Wilmington, DE

FOG Compliance in Wilmington, DE

Food service establishments in Wilmington operate under a combination of federal EPA pretreatment standards, Delaware state plumbing code, and city-level FOG ordinances. Together these rules determine how grease traps must be sized, how often they must be pumped, and what happens when a restaurant falls out of compliance.

The city follows the International Plumbing Code (IPC) for trap sizing and installation. Under Section 1003.3.4, which sizes traps by drainage fixture unit counts, grease interceptors installed in Wilmington must meet minimum capacity thresholds based on the fixtures connected to them — 3-compartment sinks, dishwashers, pre-rinse stations, wok stoves, and floor drains on the cook line. The local minimum trap size is: Per IPC 2018 sizing: peak drain flow (GPM) x 30-minute retention time.

Wilmington requires a dedicated FOG permit for any food service establishment generating fats, oils, and grease. The permit is separate from, and in addition to, the plumbing permit required at installation.

Wilmington enforces the 25 percent rule: grease traps must be pumped before the combined FOG and settled solids reach 25 percent of the trap's total liquid depth. Inspectors measure the depth with a sludge judge or dipstick, typically at surprise visits. Exceeding the threshold at inspection triggers a notice of violation and mandatory emergency pump-out, regardless of the scheduled pumping cycle. Plumbing inspector inspections per city building code. Establishments must maintain pumping logs, hauler manifests, and inspection reports on-site — missing records is itself a violation in most enforcement actions. Enforcement authority rests with the City of Wilmington Department of Licenses and Inspections / Delaware DNREC, which handles permit issuance, inspections, and hauler licensing.

For a deeper explanation of the rules this city enforces, read our guides on how grease traps work and the 25/50 pumping rule.