Grease trap pumping: 25% versus 50%

The percentage limit and maximum time between pump-outs depend on your wastewater authority. “25/50 rule” is not a single nationwide requirement.

Check your local rule first. Some authorities use a combined grease-and-solids threshold. Others specify different measures. Austin, for example, currently publishes a 90-day maximum or sooner when combined grease and solids reach 50% of wetted height. Do not apply a generic 25% threshold as if it were the Austin ordinance.

How the percentage calculation works

Where a rule uses combined layer depths, calculate (floating grease depth + settled solids depth) ÷ operating liquid depth × 100. Confirm the authority’s measurement reference, trigger wording and applicable device type.

Worked example — arithmetic, not a local permit decision

If grease measures 1 inch, solids 1.5 inches and operating liquid depth 10 inches, the combined proportion is (1 + 1.5) ÷ 10 × 100 = 25%. Whether this triggers a required pump-out depends on the applicable local wording and any shorter schedule.

Calculate your combined layer percentage

Use measurements taken safely by a suitable professional. Enter all depths in the same unit. This calculation does not set your local pumping limit or maximum service interval.

Enter measurements to calculate (grease + solids) ÷ liquid depth × 100.

Compare the result with the exact measurement definition and threshold in your permit. Find your city requirements or estimate installation sizing separately.

25% and 50% are different local thresholds

A percentage can refer to combined grease and solids, a separate layer, height or capacity. Do not assume a 50% rule means sludge alone or that it automatically accompanies a 25% rule. Read the ordinance and your permit rather than combining two unrelated thresholds.

A sourced example: Austin, Texas

Austin Water’s maintenance guidance, checked 19 October 2026, specifies pump-out at least every 90 days, earlier at a combined grease-and-solids proportion of 50% of wetted height. It also requires a city-permitted liquid-waste hauler and three years of manifests on site. Its page links the relevant code sections; these details apply to Austin, not every Texas city.

Schedule and threshold: check both

A permit can require a maximum interval and earlier cleaning when a measured threshold is reached. Keep dated measurements, pump-out manifests and any written alternative schedule. Ask the authority about variances before relying on them.

What to ask your hauler or authority

Which ordinance, permit and device-specific conditions apply to this address?
What exactly is measured and from which reference point?
What is the percentage trigger and maximum interval?
What licence and disposal documentation are required?
Are alternative schedules approved in writing?

Use an appropriate professional for measurements and servicing. Never enter a grease interceptor.

Find your local requirements

Browse city requirements · Texas city comparison · Sizing estimate and assumptions

Sizing and pumping frequency answer different questions. A preliminary sizing estimate is not a maintenance schedule or approval to install equipment.