Grease Trap for a Kitchen: Which Drains Must Connect to It?

A kitchen grease trap catches fat, oil and grease before they reach the sewer. Most Australian commercial kitchens need one, and your water authority sets the terms. The trap only treats the drains plumbed into it. Which fixtures connect matters as much as the trap itself.

Most guides explain what the trap is. This one answers the question that comes next. What actually flows into your trap, and what should stay out?

Which kitchen drains usually go into the grease trap?

Fixtures that carry food fat belong on the trap. In a typical commercial kitchen that means:

• Pot-wash and pre-rinse sinks
• Floor wastes in the cooking and wash-up areas
• Combi oven and wok station drains
• Commercial dishwashers, depending on the authority's rules

The dishwasher is the one that varies. Hot water can carry fat straight past a trap and into the sewer. Some authorities want the dishwasher connected, and others set different conditions. Your approval paperwork tells you which rule applies. If your kitchen is in Sydney, check the Sydney Water trade wastewater information.

What should stay off the kitchen grease trap?

Toilets and hand basins generally do not connect to a grease trap. They add water and solids the trap was never sized to handle. Bathroom waste normally runs to the sewer on its own line.

Mop sinks are less clear. Cleaning chemicals and grit can disturb the settled layers inside the trap. Ask your plumber or the authority before you assume either way. The national plumbing rules sit under the Plumbing Code of Australia, and local authorities add their own conditions on top.

How do you check what your trap actually serves?

Start with a simple walk-through. Here is a worked example.

Say you run a cafe with one pot-wash sink, one hand basin, a dishwasher and a floor waste under the cooking line. Run the hot tap at the pot-wash sink and listen at the trap lid. Then run a dishwasher cycle and listen again. Do the same for the floor waste with a bucket of water.

Suppose the trap gurgles for the sink and the floor waste but stays silent for the dishwasher. The dishwasher drains somewhere else. Your agreement either allows that or it does not, and if it does not, you have a compliance gap. Either way, you now have a specific question for your plumber.

A simple decision rule helps. If a fixture handles food, fat or cooking oil and does not reach the trap, ask why. If a fixture handles only body waste and does reach the trap, ask that too. Both point to a plumbing fault or an out-of-date drawing.

Take phone photos of the lid and any labelled pipes. They make the conversation with a cleaner much faster.

Does the number of connected fixtures change how often you clean it?

Yes. A trap serving a busy pot-wash sink and a dishwasher fills faster than one serving a single small sink. Trap size, the volume of fat it receives and your menu all shape the cleaning schedule. A fryer-heavy takeaway loads the trap very differently from a salad bar.

The schedule itself comes from your trade waste agreement with the water authority. Many operators do not know what theirs says. Pull it out and read the pump-out frequency before you book anything. To spot when a trap is overdue, read 5 signs your grease trap needs cleaning. If you have already skipped cleans, what happens if you never clean your grease trap explains the risks.

For the cost and frequency picture across kitchen types, see grease trap cleaning for a commercial kitchen. Sydney operators can go straight to grease trap cleaning for a commercial kitchen in Sydney.

The NSW Food Authority also expects commercial kitchens to keep waste systems clean and in working order. See the NSW Food Authority for food business requirements, and the NSW EPA for how waste is handled once it leaves your kitchen.

What is the next step once you know your setup?

Cleaners quote on trap size, service frequency, access to the trap and disposal fees. Two kitchens with the same trap can receive quite different prices. Give every cleaner the same details, tell them which fixtures connect, and send the photos.

Grease Trap Quotes sends you three quotes from licensed cleaners by SMS, usually within about a minute of your request. Get 3 grease trap quotes and compare them side by side.

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Related reading: Who Should Service Your Grease Trap? Sole Operator, Liquid Waste Firm or Quote Platform.

Related reading: Cooking Oil Waste Disposal: Where Does a Commercial Kitchen's Used Oil Go?.

Related reading: Grease Trap Servicing When You Buy or Take Over a Kitchen: The Handover Checks.