The Fog Rule

Fats, Oils & Grease
Fats, Oils & Grease

As we continue with the educational series of posts on FOG (fats, oils & grease), today we will discuss the 25% FOG rule.  Remember, you are always welcome to call me personally with any questions regarding FOG, grease traps, and/or compliance with the local & state regulations regarding wastewater, which also includes questions about Town of Mooresville’s backflow ordinance.

The 25% rule applies to grease traps and interceptors alike, make certain you do not overlook a grease interceptor during your personal monthly inspection.  The county inspector will certainly check everything, so you should as well.  Better safe than sorry!

25% FOG Rule: The FOG that floats to the top of the trap and the solids that sink to the bottom should not be in excess of 25% of the depth of the grease trap or interceptor.

The thought process behind the rule is simple; allow the wastewater enough time inside the trap to remove the FOGs (liquids and solids) effectively before entering the sewer collection system.  This can easily be controlled by scheduled cleaning.

Your cleaning schedule for FOG is greatly dependent upon your system and the amount of FOG’s you place into it.  The cleaning schedule is rather simple, clean on a prescribed schedule and record the amounts of FOG removed AND try to estimate how much FOG has entered your system during the same timeframe.  After a few months, it should be easy to understand how often to clean your trap.

The best solution to avoid FOG issues is keeping the FOG out.  In other words, set forth a process to remove the FOG in a dry cleanup and dispose of it without it ever entering the wastewater system.  Place as much as possible in the garbage and wipe as much of the grease from the equipment before using water and detergents.

If you find that your traps cannot comply with the 25% FOG rule, I can easily install better traps that can have you in compliance with the local and state wastewater regulations.


Bob ZaryBnicky
All Star Plumbing