Compliance · 2026
Commercial Kitchen Grease Trap: A Practical Guide to Grease Management
A commercial kitchen grease trap is not an optional extra. It is the piece of equipment standing between your kitchen and a blocked drain, a water-authority fine, or a closed-down site. This guide explains how grease traps work, how to size and choose one, and how to keep your drainage compliant across Kent.
The basics
Why grease traps matter for commercial kitchens
Fat, oil and grease (FOG) from cooking and washing-up cools and solidifies as it moves through pipework. Left unchecked, it builds up on pipe walls until the drain blocks completely.
A grease trap intercepts FOG before it reaches the foul water system. Wastewater enters the unit, slows down, and separates: grease and oils float to the top, solids settle at the bottom, and relatively clean water flows out to the sewer. Regularly emptied and cleaned, the trap keeps FOG out of the public network entirely.
Water companies take this seriously because FOG build-up in the public sewer causes blockages, flooding and pollution incidents. Under the Water Industry Act 1991, water companies can refuse or restrict trade effluent consent for kitchens without adequate grease management, and can recharge or prosecute operators whose discharge causes a blockage. Guidance on trade effluent consents and discharge conditions is available from GOV.UK.
For operators, the practical risk is simpler: a blocked drain on a Saturday night service, a bad smell in the yard, or an environmental health officer asking to see your grease management records during an inspection.
Specification
Choosing the right commercial kitchen grease trap
Sizing and location decisions made at the design stage save operators from expensive retrofits later.
Kitchen output
Cover numbers, menu type and peak service volume determine flow rate. A high-turnover fry-heavy menu needs a larger trap than a low-volume sandwich bar.
Under-sink or in-ground
Small passive units sit under a sink for low-volume sites. Larger kitchens usually need an in-ground or externally located gravity trap sized to the full drainage run.
Drainage layout
Existing pipe runs, invert levels and access points affect where a trap can practically be installed, particularly in older Kent high-street premises.
Emptying access
A trap that a tanker cannot reach, or that requires the kitchen to close for servicing, becomes a problem the moment it needs emptying.
Compliance
What drives grease management compliance
Grease trap rules sit across several regulatory frameworks, not one single law, which is why operators are often unclear on their obligations.
Trade effluent consent
Water companies can set conditions on FOG discharge as part of trade effluent consent, and can charge or withdraw consent where a site causes repeated problems.
Environmental health inspection
Food hygiene inspections routinely check drainage and waste management as part of structural compliance under food hygiene regulations.
Fire and safety risk
Waste fat is combustible. Poorly managed grease waste stored on site increases fire load, a factor the HSE flags in kitchen risk assessments.
Lease and landlord conditions
Many commercial leases require tenants to maintain drainage in good order, with grease trap servicing records requested at renewal or dilapidation.
Service
What a professional grease management package includes
Grease trap compliance is an ongoing service, not a one-off installation. A properly managed contract covers the full cycle.
Sizing and installation
Correct sizing against flow rate and menu, positioned for practical access and integrated with the rest of the kitchen drainage design.
Scheduled emptying
Emptying frequency set by usage rather than guesswork, with waste transfer documentation retained for inspection.
Cleaning and dosing
Regular internal cleaning and, where appropriate, biological dosing to reduce odour and slow build-up between empties.
Records and reporting
Waste transfer notes and service history kept in one place, ready for environmental health or water authority checks.
If you are unsure whether your current grease trap is the right size for your kitchen, or you are planning a refit and need drainage designed in from the start, a site survey is the quickest way to get a clear answer. Book a site survey and we will assess your drainage layout, flow rates and existing equipment before recommending a system. For kitchens undergoing a wider refit, our guide to commercial kitchen ventilation covers another area regularly checked at the same compliance visits.
Kent Commercial Kitchens supplies, installs and services grease traps for sites across Folkestone, Dover, Ashford and the wider Kent coast. Call 01304 249963 to talk through your current drainage setup.
FAQ
Grease trap questions from Kent operators
How often should a commercial kitchen grease trap be emptied?
This depends on kitchen volume and menu type, but most sites need emptying every four to twelve weeks. High-output fry sections may need more frequent servicing. Your water authority or trade effluent consent may also set a minimum frequency.
Do I legally need a grease trap?
There is no single blanket law requiring one, but water companies can impose FOG discharge conditions through trade effluent consent, and environmental health officers expect commercial kitchens to manage waste fat responsibly. In practice, most commercial kitchens need one to stay compliant and avoid blockages.
What size grease trap does my kitchen need?
Sizing is based on flow rate, which factors in sink and dishwasher output, cover numbers and peak service demand. Undersized traps overflow quickly and stop working effectively. A site survey is the reliable way to get an accurate figure rather than estimating.
Can I install a grease trap myself?
Grease traps connect into the kitchen drainage system and often need groundworks, so installation should be carried out by a qualified installer who understands both the drainage layout and local water authority requirements.
What happens if I ignore grease trap maintenance?
Neglected traps lead to blocked drains, bad odours, pest problems and possible recharge costs from your water company if a blockage affects the public sewer. Environmental health can also raise it as a non-compliance at inspection.
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