Keeping Grease in the Tank and Out of the Municipal System

Oil-Water-Grease Separators
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There are two main ways to prevent grease from escaping a grease trap/interceptor and entering a municipal system – priming the tank and using a tank configuration with both a ninety in the partition wall and an outlet tee.

Priming a Grease Trap
Before using a new grease trap or after pumping a grease trap, the tank should be primed with clean water. Priming the tank involves filling the tank with approximately twelve inches of clean water. The water level should be at or above the partition wall passage between compartments.

The tank should be primed before normal operation begins so the grease is given the chance to cool, separate, and float to the top of the tank, preventing grease from passing to the second compartment. Without the clean water added during priming, grease would settle into the bottom of the tank and pass through the partition wall into the second compartment. Once in the second compartment, some or all of the grease would make its way into the municipal sewer system, depending on the second compartment configuration.

Partition Wall Passage
Having a passage through the partition wall has a tremendous effect on how much grease passes through to the second compartment. A simple ninety that is extended down within twelve inches off the floor protects against grease from entering the second compartment.

As a worst case scenario where 100% grease was poured into the first compartment without priming before normal operation, approximately 2.2 gallons of grease would escape into the second compartment.

 
The outlet tee and the second compartment should be viewed only as emergency overflow or secondary protection and should be used in both scenarios if choosing to prime and/or with a ninety in the partition wall. When an outlet tee is installed and extended downward twelve inches off the inside floor, of that 2.2 gallons of grease that entered the second compartment in our worst case scenario, only 0.14 gallons of grease would actually exit the tank, thus dramatically reducing the amount of grease entering the municipal sewer system.
 
When used together, priming, a ninety in the partition wall, and outlet tee eliminates any grease from exiting the tank. If priming is not an option as it is not as common in most municipalities, the partition wall ninety and outlet tee reduces the amount of grease exiting the tank to near zero.