How often does a grease trap need to be pumped?

Unlike hood cleaning or suppression, grease interceptor pumping is not governed by an NFPA standard. It is governed by whoever runs your sewer system, under a local pretreatment program, and the answer genuinely differs from one city to the next.

Why there is no national number

Fats, oils and grease reaching a treatment plant are a wastewater problem rather than a fire problem, so the rules come from the water and sewer side. Local sewer authorities run pretreatment programs and write their own ordinances, and those ordinances set the pumping frequency, the reporting, and the penalties. A restaurant group operating in three cities can be under three different schedules for identical equipment.

The two ways it is usually written

1. A fixed interval. Many ordinances simply state a period, commonly thirty, sixty or ninety days, and expect the trap to be pumped at least that often regardless of how full it is. This is the easier one to comply with because it does not require judgement.
2. A capacity rule. The other common form requires pumping before accumulated grease and solids reach a set fraction of the interceptor's depth, frequently a quarter of it. This form is written into the Uniform Plumbing Code and adopted widely. It is more accurate to how the equipment actually works and much harder to prove after the fact, which is why authorities that use it usually also require records.

Some jurisdictions apply both: a capacity limit, with a maximum interval regardless. Ask which one applies to you, in writing if you can, because the answer determines whether "it was not full yet" is a defence or a violation.

The manifest is the record

This is the part that catches operators who are otherwise doing everything right. Pumping the trap is not enough. Most pretreatment programs require you to keep the hauler's manifest, the document showing who pumped it, when, how much was removed and where it was taken, and to produce those on request. Some require them retained for a specific number of years, which is more than NFPA 96 asks for hood cleaning records.

The hauler gives you this at the time, often on paper, often to whoever happens to be at the back door. That is the single most commonly lost document in this whole category.

Two agencies, not one

Your health inspector and your sewer authority are different bodies with different powers, and both may ask about the same trap. A health inspection may cite a trap that is overflowing or producing odours as a sanitation issue, while the sewer authority cares about the schedule and the manifests. Satisfying one does not satisfy the other, and they rarely talk to each other about your premises.

What to keep

Every manifest, in date order, for each location. If your ordinance uses a capacity rule, keep anything your hauler gives you recording how full the trap was, because that is the evidence that pumping happened at the right point rather than whenever someone remembered.