Grease Trap Cleaning Guide: What Every Kitchen Needs to Know

A blocked drain at 6pm on a Friday evening. The kitchen floor is flooding with grey, greasy water. You’ve got a full restaurant and nowhere for the wastewater to go.

That’s what happens when grease traps don’t get cleaned.

I’ve been called out to this exact scenario more times than I can count across Bristol’s restaurant quarter and beyond. It’s always preventable. Always.

What a Grease Trap Actually Does

Every commercial kitchen produces fats, oils, and grease. FOG, as the water industry calls it. When you wash pots, clean the fryer, or mop the floor, FOG goes into the drainage system.

A grease trap sits between your kitchen drainage and the main sewer. It slows the wastewater down, lets the grease float to the surface, and allows the cleaner water to pass through to the sewer.

Without a grease trap, FOG goes straight into the sewer. It cools, solidifies, and sticks to pipe walls. Over time, it blocks the sewer. That’s how fatbergs form. Bristol Water and Wessex Water are very clear about this: commercial kitchens must have grease management in place.

There are two main types.

Under-sink grease traps. Small units fitted beneath pot wash sinks. Common in smaller kitchens. They hold 30-100 litres typically.

In-ground grease traps. Larger tanks buried outside the building. These serve the whole kitchen drainage system and hold several hundred litres or more. More common in bigger operations.

Both do the same job. Both need cleaning.

How Often to Clean Your Grease Trap

The answer depends on your kitchen’s output and the size of your trap. But here are the working guidelines.

Busy restaurants, takeaways, and pubs cooking high-grease menus: every 4-6 weeks. If you’re frying heavily every day, grease accumulates fast.

Standard commercial kitchens with moderate output: every 2-3 months.

Light-use kitchens in offices, small cafes, or facilities doing limited cooking: every 3 months.

The rule of thumb: a grease trap should be emptied when it’s 25% full of FOG. Any more than that and it stops working effectively. Grease starts passing through to the drainage system, which defeats the purpose entirely.

If you’re not sure, check it. Open the lid. If there’s a thick layer of grease on top and sludge at the bottom, it’s time.

Honestly, most of the kitchen managers I talk to have no idea when their grease trap was last cleaned. Some didn’t know they had one. That’s not a criticism. Nobody teaches you this stuff when you open a restaurant. But it matters.

What Happens If You Don’t Clean It

Blocked Drains

The most immediate consequence. Grease passes through the overloaded trap, builds up in downstream pipes, and blocks them. Drain unblocking is expensive, disruptive, and usually happens at the worst possible moment.

Sewage Backup

When drains block completely, wastewater backs up into your kitchen. This is a food safety emergency. You may need to close until it’s resolved. An EHO finding sewage in a food preparation area is about as bad as it gets.

Fines from the Water Company

Wessex Water and Bristol Water can and do prosecute businesses that discharge excessive FOG into the sewer system. Fines run into thousands. They can also require you to install grease management equipment at your cost.

Odours

A full grease trap smells. Badly. Decomposing FOG produces hydrogen sulphide. The rotten egg smell. It comes up through your drains, into your kitchen, and sometimes into the dining area. Not what your customers want with their dinner.

Pest Attraction

Rats, flies, and cockroaches are attracted to grease and decomposing food waste. A neglected grease trap in the yard is an open invitation.

Failed Inspections

Environmental Health Officers check grease management as part of kitchen inspections. A poorly maintained grease trap suggests wider hygiene management problems. It affects your food hygiene rating.

The Professional Cleaning Process

Here’s how we clean a grease trap. No surprises.

1. Assessment. We check the trap type, size, condition, and current fill level. First visit, we’ll also check the inlet and outlet connections and the general drainage run.

2. Pump out. The contents are pumped out using a vacuum tanker or, for smaller under-sink traps, manual removal into sealed waste containers. FOG waste is classified waste and must be disposed of properly with documentation.

3. Scrape and clean. The trap interior is scraped clean of hardened grease deposits on walls, baffles, and fittings. This is the bit that makes the difference between a proper clean and just emptying it.

4. Flush and test. We flush the trap with clean water and check the flow through to make sure everything is draining correctly. Inlet and outlet pipes are checked for blockages.

5. Inspect. We check the trap for damage. Cracked baffles, corroded fittings, damaged seals. Small problems caught early are cheap fixes. Small problems ignored become big ones.

6. Record. Date of clean, condition found, waste disposed, any issues noted. This goes into your records for compliance purposes.

The whole job takes 30-60 minutes for a standard trap. Larger in-ground systems take longer.

We work early mornings or after service to avoid disrupting your kitchen operations. Most of our Bristol restaurant clients have us come in between 6am and 8am before the kitchen opens.

Setting Up a Schedule

The simplest approach is a standing booking. We’ll come every month, every 6 weeks, or every quarter depending on what your kitchen needs. You don’t have to remember. You don’t have to book each time. We just turn up, do the job, and leave the paperwork.

We’ll adjust the frequency if needed. If we’re arriving and the trap is nearly empty, you might be fine going longer between cleans. If it’s overflowing, we need to come more often.

It’s one of those jobs that costs relatively little when done regularly and costs a lot when neglected. A quarterly grease trap clean is a fraction of the cost of one emergency drain unblocking call, let alone the consequences of a sewage backup during service.

Get Your Grease Trap Sorted

Bristol Cleaning Heroes cleans grease traps for restaurants, pubs, hotels, care homes, and food production kitchens across Bristol. We handle the waste disposal documentation, keep your compliance records current, and flag any problems before they become emergencies.

We’re based in BS10 and insured to £2 million.

Call 07985 505061 or email hello@bristolcleaningheroes.co.uk.