What Is a Restaurant Grease Trap? A Selection, Placement and Maintenance Guide

How does a grease trap work?

When wastewater from sinks and suitable kitchen equipment enters the tank, flow velocity drops. Free fat and grease collect on the surface, heavier solids settle to the bottom, and relatively treated water moves toward the outlet. Baffles and flow regulators reduce short-circuiting, giving more time for separation.

A grease trap is not a waste disposer and does not chemically destroy grease. Emulsified fine fat droplets or the wrong detergent can reduce separation efficiency — kitchen practices and equipment selection should be considered together.

Which lines connect to a grease trap?

Connection scope depends on the project and local infrastructure requirements. Prep and wash sinks, pot-washing stations and some grease-producing equipment can be connected. Toilet waste, rainwater and high-flow discharges unsuited to the unit's design should not share the same line.

A dishwasher's very hot, detergent-laden discharge can emulsify grease or raise unit temperature. This connection should be assessed with manufacturer data, project calculation and local sewer-authority requirements.

What data determines capacity selection?

• Volume and drain time of connected sinks and equipment
• Total flow of sources that can operate simultaneously
• Daily and peak-hour meal/cover count
• Menu's grease load and cooking methods used
• Wastewater temperature, detergent and cleaning habits
• Amount of solid food residue and use of pre-strainers
• Planned service interval for emptying and cleaning
• Local water/sewer authority's discharge conditions

A smaller unit isn't always more economical — it needs frequent emptying and maintenance. An oversized unit wastes space, investment and cleaning effort. The calculation should be verified by a competent utilities designer and manufacturer data.

Where should the grease trap be placed?

The unit should sit as close to the grease source as possible, protected from freezing and excess heat, with ventilation and service access resolved. Lids must fully open, accumulated waste must be removed safely, and cleaning must not contaminate the kitchen operation.

For units inside an enclosed kitchen, sealing, odour control, floor drainage and a hygienic service procedure matter especially. For outdoor or buried large systems, vacuum-truck access, vehicle load, level difference and backflow risk are checked in the project.

How is maintenance frequency determined?

Maintenance can start on a calendar, but the real interval should be optimised by observation. The unit should be emptied before the grease and solids layer seriously reduces separation volume. Measuring the level frequently in the first weeks helps find the business-specific interval.

• Check inlet/outlet flow, odour and backflow signs.
• Measure surface grease layer and bottom sludge level safely.
• Remove grease and solids per authorised waste-management procedures.
• Clean baffles, inlet/outlet fittings and gaskets without damage.
• Refill the tank with suitable water and check sealing and flow.
• Record date, level, amount removed and any faults found.

Common causes of blockage and odour

• Pouring food scraps down the sink and relying solely on the grease trap
• Enclosing the unit under a cabinet or fixed equipment with no access
• Only performing maintenance once overflow or odour appears
• Assuming more detergent dissolves the grease away
• Wrong level, insufficient venting, or missing backflow protection
• Choosing based only on connection diameter, without a capacity calculation