Specialty Plumbing Systems

Grease Traps (Grease Interceptors)

A grease trap (grease interceptor) is required on drainage from commercial kitchen fixtures to prevent fats, oils, and grease (FOG) from entering the municipal sewer system. Grease solidifies in pipes and causes blockages.

FOG

Fats, Oils & Grease - Must Be Intercepted

Gravity

Grease Floats - Trapped at Surface

Monthly

Typical Pumping Schedule

How Grease Traps Work

Grease traps use a simple principle - grease is lighter than water and floats. Wastewater enters the trap, slows down, and grease rises to the surface where it is retained. Cleaner water exits from the bottom of the trap to the sewer.

Under-counter traps - small units for individual fixtures
In-ground interceptors - large units for entire commercial kitchens
Sizing is based on fixture drainage flow rates
Regular pumping is required to prevent trap capacity from being exceeded

Floor Drain Trap Primers

Floor drains in commercial and institutional buildings often go weeks or months without receiving water flow. Without regular flow, the trap seal evaporates and sewer gas enters the building. A trap primer automatically adds water to maintain the seal.

Trap Primer Types

Pressure-activated - triggers when supply line is used

Electronic - timer-based water delivery

Passive (trap seal primer) - uses fixture waste flow

Where Required

Commercial floor drains

Mechanical rooms

Any floor drain not receiving regular flow

Emergency drains in mechanical spaces

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Exam Tip

When the exam asks why sewer gas enters through a floor drain, the answer is evaporated trap seal. The solution is a trap primer to maintain the water seal.

Key Takeaway

Grease traps intercept FOG from commercial kitchen drainage by allowing grease to float and be retained. Trap primers maintain water seals in floor drains that do not receive regular flow, preventing sewer gas entry from evaporated trap seals.

Grease Traps & Floor Drain Trap Primers