How often must a grease trap be cleaned in Nashville?

The requirements

Metro Water Services runs the FOG — fats, oils and grease — program for Nashville, and enforces grease interceptor installation, routine maintenance, certified hauler manifest use and three-year record retention.

Unit type	Minimum service interval
Grease trap (typically smaller, under-sink)	At least every 30 days
Grease interceptor (larger, often underground)	At least every 90 days

And overriding both, the 25% rule: the unit must be cleaned when the combined volume of FOG and settled solids reaches 25% of the unit’s capacity — whichever comes first.

Why the minimum is not the answer

The most common compliance failure is treating the calendar minimum as the target.

A kitchen producing heavy FOG will hit 25% well before its 30 or 90 day mark. High-volume operations — fried chicken, fish, large quantities of rice or pasta — routinely need service more frequently than the minimums to stay under the threshold.

Servicing on the minimum interval while sitting at 40% for the last two weeks of every cycle is not compliant. It is a scheduled failure that happens to have a service record attached.

Under-sink units need weekly attention

Separate from the 30-day service requirement, under-sink grease traps should be cleaned weekly. And there is a useful diagnostic built into that: if the unit is more than half full at the weekly check, the cleaning frequency needs to increase.

That is the cheapest early warning available. A kitchen whose trap is at 60% every week is telling you it needs a shorter cycle before it tells you by blocking the line mid-service.

The paperwork is part of the requirement

This trips up more kitchens than the intervals do.

Metro requires certified hauler manifests for grease service, and three-year record retention. A manifest is issued at each service and evidences that the material was collected by a certified hauler and disposed of lawfully.

When an inspector asks, the manifest file is what answers. A clean trap with no documentation is not a compliant trap — it is an undocumented one, and the burden of proof sits with the business.

Setting a frequency that works

The realistic approach is to start at the minimum for your unit type, measure against the 25% threshold at each service, and shorten the cycle if you are consistently above it.

Things that push you toward a shorter interval:

• Fried food, particularly chicken and fish
• High volumes of rice and pasta, which contribute solids as well as FOG
• An undersized unit for the covers served
• Extended service hours or seven-day trading
• Seasonal peaks

What a proper service includes

• Full pump-out of FOG, water and settled solids — skimming the floating layer and leaving the solids is what turns a serviced trap into a failed inspection
• Baffle and flow-control fitting checked and cleared
• FOG and solids measured against the 25% threshold
• Certified hauler manifest issued
• Frequency reviewed against what was actually found

Bottom line

30 days for traps, 90 for interceptors, and clean at 25% regardless. Check under-sink units weekly, and shorten the cycle if they are over half full. Keep every manifest for three years. Call (615) 234-9048 to set a schedule against your actual FOG production rather than the minimum.