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Grease Trap Management in Dorchester

Emptying and maintaining grease separation for commercial kitchens.

Call 0330 133 1625 Request a quote

What is a grease trap and what does it do?

A grease trap is a tank fitted to a kitchen's waste pipe that holds back fats, oils and grease, so they collect in the trap instead of setting hard inside the drain further along.

Waste water from sinks and dishwashers enters the trap and slows down. As it cools, fat floats to the top and food solids settle to the bottom, while the clearer water in between flows out to the drain. Baffles inside stop the floating fat from leaving with it.

The trap only works while there is room in it. Once the fat layer and sludge take up too much of the tank, waste passes straight through, and the fat solidifies in the pipe beyond, where a blockage is far more disruptive to clear. We empty and service grease traps and separators for kitchens in and around Dorchester, so they keep doing that job.

Is a grease trap a legal requirement in the UK?

There is no single UK law that says every food business must have a grease trap, but several rules have much the same effect for any kitchen sending fat to the sewer.

  • Under section 111 of the Water Industry Act 1991, it is an offence to put anything into a public sewer that is likely to interfere with its flow. Fat that builds up into a sewer blockage falls into that.
  • Building Regulations Approved Document H says drainage serving commercial hot food premises should have a grease separator or another effective means of grease removal. That applies when drainage is built or altered, such as in a new fit-out.
  • A planning condition or the sewerage company may require one for a new food business.

In practice, a kitchen without effective grease control carries a real risk if a sewer blocks.

What happens if a grease trap isn't maintained?

An overdue grease trap stops holding fat back, so blockages form in your drain or the public sewer, and the kitchen starts to smell; the trap itself can also back up into the sinks.

The usual sequence is slower sinks, then foul odours as the trapped fat and food go rancid, then a blockage at a floor gully or the first chamber outside. In a busy service that can close the kitchen.

If fat from your premises contributes to a public sewer blockage, the water company can investigate where it came from. Clean-up costs can be recovered from the business responsible, and in serious cases a prosecution under the Water Industry Act is possible. Regular emptying and records showing it was done are the simplest protection.

What are the signs a grease trap needs emptying?

The most reliable sign is a trap whose fat and sludge layers are taking up a large part of the tank; slow sinks and a rancid smell usually mean it is already overdue.

Other things that point the same way:

  • Sinks or dishwasher outlets draining more slowly than usual
  • A sour, rancid smell near the trap or the kitchen gullies
  • Fat visible in the outlet pipe or in the chamber downstream
  • Water rising in the trap lid or around a floor gully
  • More covers or a menu change since the interval was last set

If you have a lift-off lid on an under-sink unit, a quick look each week tells you a lot about how fast your trap fills.

How often should a grease trap be emptied?

How often a grease trap needs emptying depends on its size and on how much fat the kitchen produces. A busy kitchen with a small trap may need it every week or two; a quiet one with a large separator may go months.

The things that decide it are the volume of the trap, the number of covers, the menu, the cooking methods and the equipment connected to it. Frying, roasting and dishwashers running hot all push the interval shorter.

The right interval is set by watching how your trap actually fills, not by copying another kitchen. We note the depth of fat and sludge at each visit and suggest an interval from that, then adjust it as the pattern becomes clear. A trap emptied too late fails, and one emptied too early is money wasted.

How we empty and service a grease trap

We remove the fat, sludge and water from the trap, clean it, check it is working properly and leave you a record and the waste paperwork.

  • We agree a time outside service, so the kitchen is not using water while the trap is open
  • The lid is removed and the depth of fat and sludge is measured and noted
  • The contents are removed, by hand for small units or by tanker for larger separators
  • The tank walls, baffles and inlet and outlet are scraped and cleaned
  • Seals, lids and any baskets are checked, and faults are reported to you
  • The trap is refilled with clean water so it works from the first use
  • The area is cleaned down and you get the visit record and waste transfer note

If the outlet drain shows fat build-up, we tell you, because that means grease has been getting past.

How long does grease trap emptying take?

A small under-sink grease trap can often be emptied and cleaned in under an hour; a large below-ground separator emptied by tanker takes longer, depending on its size and access.

How long it takes also depends on how full the trap is, how hard the fat has set and whether the inlet and outlet pipes need clearing as well. A trap that has gone far past its interval takes more cleaning than one serviced on time.

With visits planned before opening or after closing, the work usually fits within the time the kitchen is not in use.

Grease trap, separator or interceptor: what is the difference?

They do the same job at different sizes. A grease trap usually means a small unit under or beside a sink, while a grease separator or interceptor is a larger tank, often below ground, serving a whole kitchen.

Small traps suit a cafe or a kitchen with one or two sinks. Larger separators handle the flow from several sinks, dishwashers and floor gullies, and are usually emptied by tanker.

There are also automatic grease removal units, which skim fat off into a container that staff empty, often daily. These still need their sludge removed, their skimming parts checked and the container handled properly. Whatever you have, it only protects the drain if it is sized for the flow and emptied before it is full.

What grease trap maintenance can and can't fix

Regular emptying keeps fat out of your drains and stops the trap itself smelling or backing up. It cannot compensate for a trap that is too small, or clear fat that has already built up in the drain beyond it.

If the drain after the trap is already lined with fat, it needs cleaning separately, and we will tell you if we see that. If a trap fills so fast that no sensible interval keeps up, it may be undersized for how the kitchen now operates, which is worth knowing before a change of menu or extra covers.

A trap with a damaged baffle, missing lid seal or broken outlet will not work properly however often it is emptied. Those faults are reported to you with what we found.

How much does grease trap management cost?

The cost depends on the type and size of trap, how full and set the fat is, whether a tanker is needed and how often it is emptied.

As a guide, most commercial grease trap cleans cost between £150 and £350 per visit, depending on the size of the trap and where it is.

You agree a fixed price for the visit before we start, and if you set up regular emptying, the price for each visit is agreed at the outset as well. If we open the trap and find something that changes the job, such as an outlet blocked with set fat, we stop, show you and agree the extra work before doing it.

Waste transfer notes and maintenance records

Waste removed from a grease trap is your business's waste, so the duty of care applies: it must go to a registered waste carrier, and each transfer needs a waste transfer note that you keep.

In England, waste transfer notes should be kept for at least two years. They show where the waste went and who took it, which matters if anyone asks how your kitchen disposes of its fat.

Alongside the waste paperwork, you get a record of each visit: the date, the depth of fat and sludge found, the condition of the trap and any recommendation. Together, those documents let you show an environmental health officer, landlord, insurer or the water company that the trap is maintained, from a file rather than from memory.

Kitchen habits that keep a grease trap working

The trap works best when as little fat as possible reaches it, so scraping, wiping and collecting oil before anything goes in the sink makes the biggest difference.

  • Scrape plates and pans into food waste, and wipe greasy pans with paper before washing
  • Collect used cooking oil in a container for a waste oil collector, never down the sink
  • Keep sink strainers in place so food solids do not fill the trap
  • Avoid pouring very hot water or strong degreasers through the trap, because they melt or break up the fat, which then reforms in the drain beyond
  • Keep the lid sealed and the area clear, so the trap can be checked
  • Note any change in menu or covers, because it changes how fast the trap fills

These habits work whatever size of trap you have.

Covering Dorchester & the local area

We provide grease traps throughout Charminster, Martinstown, Crossways, Puddletown, Broadmayne, Poundbury and the surrounding area. Call 0330 133 1625 for a free, no-obligation quote.

How it works

Simple, transparent process

  1. 1

    Tell us what’s happening

    Call and describe what you’re seeing — a slow sink, a gurgle, a smell or standing water. It usually tells us a lot before we arrive.

  2. 2

    We find the cause

    We clear enough to get flow back, then work out why it blocked — because a drain that blocks twice has a reason.

  3. 3

    A price before the work

    If it needs more than a clear — a repair, a lining, a survey — you get the price and the reason before we start it.

  4. 4

    You see the evidence

    Where we survey, you get the footage. Where we repair, you see the before and after.

Don't let it get worse

Get expert help right now

Tell us what the drain is doing and we will explain what is likely causing it and what the work involves.

Call 24/70330 133 1625

Other services

Emergency Unblocking

A drain that has stopped completely, water backing up or sewage escaping — the jobs that cannot wait until Monday.

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Blocked Sinks

Kitchen sinks, basins, baths and showers draining slowly or not at all.

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Drain Cleaning

Clearing build-up before it becomes a blockage — for properties that keep having the same problem.

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Grease Traps: common questions

Can grease traps be emptied outside trading hours?
Yes. Because we work 24/7, emptying can be booked for early mornings, late evenings or days the kitchen is closed. Planning it outside service matters, because the trap cannot be used while it is open, and the work is easier and cleaner with no water running through. Tell us your service times and delivery windows when you book, and we will fit the visit around them.
Can you set up a regular grease trap emptying schedule?
Yes. We agree an interval with you, based on how quickly your trap fills, and arrange visits on that basis. The interval is checked against what we find each time, and if the trap is consistently less full or more full than expected, we suggest a change and agree it with you. Regular visits also build the record of maintenance your kitchen may be asked for.
What size grease trap does my kitchen need?
Size depends on the peak flow of waste water from the sinks and appliances connected to it, the water temperature, and the amount of fat in it, which depends on the menu and covers. The British and European standard for grease separators, BS EN 1825, sets out a sizing method. An undersized trap fills too fast to keep up, so get the sizing checked before a fit-out or a change of menu.
Can kitchen staff empty a small under-sink grease trap themselves?
Some kitchens do empty small passive traps themselves, following the manufacturer's instructions and wearing gloves. The waste must not go back down a sink or drain, and it remains your business's waste under the duty of care, so it has to be disposed of properly. Larger traps and separators, and any trap that has set hard, are better handled with the right equipment.
Does used cooking oil go into the grease trap?
No. Used cooking oil from fryers and pans should be collected in containers and taken away by a waste oil collector, not poured down a sink. A grease trap is designed to catch the fat left on plates, pans and utensils during washing, not bulk oil. Pouring oil into the trap fills it very quickly and sends fat into the drain beyond.
Who is responsible for the grease trap in a leased kitchen?
Usually the business running the kitchen, because it is the one producing the fat, but check your lease. Some landlords keep responsibility for the trap as equipment and recharge the cost, while the tenant remains responsible for how the kitchen is used. Whoever arranges emptying should keep the visit records and waste transfer notes, so both parties can see the trap is maintained.
What happens if fat from my kitchen blocks the public sewer?
Water companies investigate fat blockages in sewers and can trace them back to the premises responsible. In Dorchester that is Wessex Water. A business found responsible may be asked to pay for clearing the sewer and for any damage caused, and serious or repeated cases can lead to prosecution. Records of regular grease trap emptying are the clearest evidence that your kitchen was doing its part.
Why does my grease trap smell?
A grease trap smells when the fat and food solids in it have been sitting long enough to go rancid and start breaking down, which usually means it is overdue for emptying. A broken lid seal or a dry trap after a long closure can also let odour escape. If the smell continues after emptying, the drain beyond the trap may be holding fat as well.
Do automatic grease removal units still need servicing?
Yes. An automatic unit skims fat off into a collection container, but food solids and sludge still settle in the tank, and the heating and skimming parts can fail. The container must be emptied as the maker specifies, and the tank needs cleaning periodically. If a unit has stopped skimming, it behaves like an overfull trap and passes fat straight into the drain.
Does a kitchen that hardly fries still need its grease trap emptying?
Yes, though usually less often. Fat comes from far more than frying: butter, sauces, dairy, roasting juices and meat all leave grease on plates and pans, and dishwashers wash it into the trap. A lighter menu may justify a longer interval, which the depth of fat found at each visit will show. It is not a reason to stop emptying altogether.