Fats, Oils and Grease: Keeping Restaurant Drains Flowing

Fats, oils and grease (FOG) block restaurant drains because they are liquid when hot but cool, set and stick to the inside of the pipe further down the line. Over time they bind with food waste and wipes to form hard deposits that narrow the drain and eventually stop it. The fix is to keep FOG out of the drains in the first place, with good kitchen habits and a properly maintained grease trap.

How fatbergs form

Hot washing-up water carries grease off pans, plates and trays. Once it leaves the building the water cools, the grease separates and clings to the pipe wall, especially at joints, bends and any rough or damaged sections. Every service adds another layer.

Food particles, starch and wet wipes get caught in that layer. The fats can also react with minerals in the waste water and harden into a soap-like material. The result is a growing mass that reduces the pipe’s capacity until it blocks. When this happens in the public sewer, the mass can become huge: the so-called fatbergs that water companies remove from London’s sewers.

Why this matters in Covent Garden

Covent Garden and the West End have a high concentration of restaurants, cafés, bars and hotel kitchens, many of them in older buildings with long-established drains and sewers. That means a lot of commercial kitchens discharging into a shared network. A single kitchen with poor grease management can block its own drain, but it can also contribute to blockages that affect neighbours, basements and the street.

For a busy kitchen, a blocked drain mid-service can mean a closed kitchen, flooded floor drains and an unpleasant smell in the dining room. Prevention is cheaper than an emergency.

The legal side in England

Section 111 of the Water Industry Act 1991 makes it an offence to put anything into a public sewer, or into a drain or sewer that connects to one, that is likely to interfere with the free flow of its contents or damage the sewer. Fats, oils and grease fall squarely into that. The water company (Thames Water in London) can investigate blockages, trace them back to the premises responsible and take action.

Beyond that, food businesses are expected to have suitable grease management in place. For new or refurbished commercial kitchens, building regulations guidance points towards fitting a grease separator or other effective means of removing grease. Used cooking oil is commercial waste and should be collected by a registered waste carrier, not poured away. If you are unsure what applies to your premises, ask your local authority or Thames Water for their current guidance.

Grease traps and separators

A grease trap (or grease separator) sits between the kitchen fittings and the drain. It slows the waste water down so it cools and the grease floats to the top, while solids settle at the bottom and the cleaner water passes on to the drain. Units range from small under-sink traps to larger separators installed below ground outside the building.

Other options include grease removal units that skim off the collected fat automatically, and dosing systems that add biological products to the drain. Dosing can help, but it does not replace a trap or good kitchen practice.

Maintenance is what makes them work

A grease trap that is never emptied stops working. Once it is full, grease passes straight through to the drain. How often it needs emptying depends on its size and how much cooking you do, so follow the manufacturer’s guidance and adjust based on what you find when it is opened. Keep a log of every clean, with the date and who did it. It helps you spot trends and shows you are managing FOG responsibly.

A practical kitchen checklist

• Scrape plates, pans and trays into the food waste bin before they go near the sink or dishwasher.
• Wipe greasy pans and trays with kitchen roll before washing.
• Collect used cooking oil in sealed containers for a registered waste carrier. Never pour it down a sink or floor drain.
• Fit sink strainers and floor drain baskets, and empty them into food waste.
• Empty and clean the grease trap on a regular schedule and record each clean.
• Don’t pour hot water or degreaser after grease to wash it away. It moves the problem further down the pipe.
• Train every new starter, including kitchen porters and evening staff, on what goes where.
• Watch for early signs: slow sinks, gurgling floor drains, smells and grease in outside chambers.
• Book planned drain jetting for kitchen drains rather than waiting for a blockage.

How we clear and prevent FOG blockages

For an active blockage, we lift the chambers to find it, then clear the line with high-pressure water jetting. Jetting scours grease off the pipe wall instead of just opening a channel through it, so the drain runs at closer to its full bore. Where a drain blocks repeatedly, a CCTV drain survey shows whether the cause is grease build-up alone or a defect such as a dip, a displaced joint or a damaged section that catches it.

We can also set up planned maintenance visits, timed around your service, so jetting happens before problems start rather than in the middle of a Saturday night.

Our commercial drainage team works with restaurants, cafés, bars and hotels across Central London, day and night. For a free quotation for planned maintenance, or help with a blocked kitchen drain right now, call 020 3670 7648.