Grease traps in hotel kitchens: what they do, cleaning and local rules

A grease trap is a chamber that slows kitchen wastewater so fats, oils and grease float to the top and food solids settle, while the clearer water in the middle flows to the sewer. It holds grease; it does not destroy it. Cleaning frequency comes from measuring the layers, and the rule comes from your local water authority.

It is 20:00, the banquet is on its main course, and the dish pit is backing up. The drain is not blocked at the grid. It is blocked thirty metres away, in a chamber nobody has opened since spring. After reading this you will know what that chamber does, which lines should run through it, how to size and empty it, where the waste must go, and which authority's text actually sets the duty in your city.

What does a grease trap actually do?#

It separates fats, oils and grease from kitchen wastewater before that water leaves the building, so the sewer pipe stays open and the network receives less grease.

The mechanism is gravity, not filtration. The chamber slows the flow, grease rises because it is lighter than water, food solids sink, and the middle layer of water flows out to the sewer. Retention time is the whole design: a hotel grease trap that is too small, or too full, gives the water no time to separate, and grease leaves with it.

It holds grease; it does not destroy it. Everything the trap catches has to be pumped out and carried away. It also does not catch dissolved detergents, dissolved organics, fine suspended solids, or fat that hot water and strong detergent have emulsified into the flow.

You will meet two common shapes, one principle. A small unit sits under a pot sink; an outdoor interceptor chamber sits in the ground and serves the whole kitchen line. The scale and the emptying routine differ, the physics does not.

The failure is quiet. Grease narrows the pipe over months; slow drainage and gurgling at the lowest drain come first, and a backup follows during service.

Where does the grease trap belong in the line?#

On the lines that carry grease: pot sinks, pre-rinses, dishwashers, combi oven drains and kitchen floor drains. Not on toilets, hand basins or rainwater.

Draw the line before you buy anything. List every drain and every appliance that discharges in the kitchen and dish area, then decide which ones pass through the trap. The trap sits before the parcel manhole, on the hotel's own property, so it can be reached, opened and pumped without digging up the street. İSKİ's subscriber regulation places it there for restaurants, food production facilities and car washes (Article 50(1)(b)).

Never route rainwater, irrigation water or clean water through it. Dilution pushes the grease straight out of the trap. Toilets and hand basins go directly to the sewer; they add solids and flow the trap was never sized for.

Access is part of the position: a cover wide enough for the pump hose, room for a person to stand and work, and a lid that can be lifted safely. Dishwasher water is hot and carries detergent, which can emulsify fat, so ask the installer whether the machine line enters the trap directly or passes a solids interceptor first. A trap also needs air: a blocked or missing vent turns it into an odour source in the middle of the kitchen.

How is a grease trap sized?#

By calculation from the kitchen's peak flow and the retention time the trap needs, not by choosing the unit that happens to fit the space.

The installer needs four inputs: which fixtures discharge into the trap, their flow rates, the dishwasher's rating, and the peak hour rather than the daily average. Ask for the calculation in writing, with the standard it follows. EN 1825 is the European standard for grease separators; if your installer names it, ask which part and which size class.

Undersizing fails silently. The water passes too fast, separation does not happen, and grease reaches the sewer while the trap looks perfectly normal. Oversizing has its own cost: the water cools, grease hardens on the walls and around the outlet, and pumping becomes harder and messier.

In a retrofit there may be no fall and no space. A smaller trap on the worst lines plus a strict cleaning routine can be the honest answer, provided the decision is written down and signed. And the trap is not the only lever: sink strainers, scraping food into the bin before washing and a grease-free pre-rinse cut the load that reaches it.

How often should a hotel grease trap be cleaned?#

Set the interval from your own measurements, then shorten it for peak season. A calendar copied from another hotel tells you nothing about your kitchen.

Measure, do not guess. A dip stick or sludge judge through the cover shows the thickness of the floating grease layer and of the settled solids. A workable starting threshold, to be agreed with your installer and waste contractor, is to pump when grease and solids together reach about a quarter of the liquid depth; then adjust from your own readings.

Record every reading with date and depth. After two or three months you have a real interval for your kitchen, and a second, shorter one for banquet season.

Cleaning means pumping out grease, solids and liquid, scraping the walls and the baffle, checking the inlet and outlet tees, and refitting the baffle correctly. Skimming the top is not cleaning: it leaves the settled solids and the hardened grease that actually cause the blockage. Trained in-house staff can handle a small under-sink unit; an outdoor interceptor is normally pumped by a licensed waste contractor. Ask your water authority what it expects for your case.

Where does the grease trap waste go?#

To a licensed waste contractor who takes it to a permitted treatment or disposal facility, with a transfer record naming the volume and the destination. Not to the sewer, not to the general waste bin, not to the garden.

Putting the grease back into the sewer defeats the trap and can breach the same discharge rules that required it. The general waste bin is not an option either: liquid grease leaks, attracts pests, and is not ordinary municipal waste. Your waste records will not reconcile.

The transfer record is the evidence: date, volume, contractor, vehicle and destination facility. Keep the copies; they are what you show when someone asks where the grease went. Volume is also a management number: litres pumped per month, read against covers or banquet events, shows whether the kitchen is improving or whether something is bypassing the trap.

If the hotel tracks waste under a zero waste system, grease trap waste belongs in that record next to food waste and collected cooking oil. Ask the contractor where the waste actually ends up, and keep the written answer on file. For the wider record-keeping duties, see our guide to zero waste rules for hotels in Türkiye.

Who sets the grease trap rule, and where do you read yours?#

Your local water and sewerage authority, through its wastewater discharge regulation and its subscriber regulation. There is no single national article a hotel can read and be done with.

İstanbul, as a worked example: İSKİ's discharge regulation, General Assembly decision No. 3 of 16 January 2013, in force since 24 January 2013, with Articles 3 to 6 and 8 to 14 amended by decision No. 13 of 13 June 2023, requires food production businesses to install a grease trap under Article 12(17), and Article 12(18) gives them at most three months to do so, without asking them to build a pretreatment plant. The same regulation counts wastewater from service sectors such as schools, hospitals and hotels as domestic wastewater (Article 3), and bars hazardous, toxic, flammable or explosive substances, treatment sludge and solids that block the network (Article 5).

The in-building placement rule sits in İSKİ's subscriber regulation, General Assembly decision 2018/8 of 16 May 2018, in force since 31 May 2018, current text published September 2026: restaurants, food production facilities and car washes need a grease trap or a mud trap before the parcel manhole (Article 50(1)(b)). Article 56 repealed the earlier plumbing regulation.

These are İstanbul's rules. A hotel in Antalya, İzmir, Muğla or anywhere else is governed by its own authority's text; do not assume İSKİ's wording travels. To find yours, search the authority's website for its wastewater discharge regulation and its subscriber services regulation, and look for the grease trap, pre-treatment and placement clauses. Ask in writing whether the duty covers your facility type, what the deadline is, whether a discharge or connection permit is needed, and who inspects. Confirm dates, penalties and your own case with the authority and your legal or technical adviser before you buy or build. The kitchen-side duties are covered in our article on hotel kitchens and food law in Türkiye.

What goes on the log sheet, and why does the kitchen smell?#

A one-page log with the date, the measured layer depths, the volume pumped and the contractor's record number. Odour almost always means the trap is overdue, the vent is blocked, or something is bypassing the trap.

A log that only says "cleaned" is useless. The depths are what let you change the interval with evidence instead of opinion. Tie the trap to the hotel preventive maintenance plan so the check survives a change of kitchen manager or a busy season.

Odour causes, in order of likelihood: overdue emptying and anaerobic conditions, a missing or wrongly refitted baffle, a blocked or missing vent, grease left on the walls above the water line, a dry trap in a seasonal kitchen, and a line that bypasses the trap entirely. Slow drains at the lowest point, gurgling and a smell that worsens after service are late signals. The measurement is the early one.

Raise the fix as a work order with a photo, a named owner and a deadline, not a verbal note at shift handover; our guide to hotel maintenance work orders covers the flow. Review the log once a month against the pump-out volumes: a sudden drop in volume usually means the trap is being bypassed, not that the kitchen got cleaner.

What to do next#

Open your trap this week, measure the two layers, and write the numbers down. That single reading starts the interval, the log and the evidence you will need later. The rest follows in order: the trap does one job, holding grease so it cannot reach the sewer; sizing and cleaning decide whether it actually does that job; the waste leaves through a licensed contractor with a record; and the duty itself comes from your own water and sewerage authority, whose text you should read before you buy, build or defend anything.