Before it reaches about a quarter full, which for most kitchens lands somewhere between monthly and quarterly. Menu matters more than seating: fryers and griddles fill a trap far faster than the same number of covers coming off a grill.
Why the interval matters more than the size
A trap at a quarter full is already passing grease
The rule most kitchens are held to is that a trap gets serviced before the combined grease and solids reach about a quarter of its working depth. Past that point the retention time drops below what the trap needs to separate, and grease leaves with the flow whether the chamber looks full or not.
Which is why a bigger trap is not a substitute for a shorter interval, and why we size the schedule from your actual fill readings rather than from a standard frequency. A fryer-heavy kitchen at forty covers can need more frequent service than a hundred-cover dining room that mostly grills.
Grease that gets past the trap does not disappear. It cools and lines the pipe, which is how a cleaning contract turns into a blockage call, and on a septic property it is also how solids reach the drain field. Intervals and paperwork are covered on grease trap compliance.
One quarter full
Trigger
Left on site
Manifest
Outside service hours
Timing
