What a grease trap needs from a busy kitchen

Grease trap upkeep comes down to three things: the right size, a reachable spot and a cleaning schedule. Skip any one and fat sets like candle wax in your drain.

Interview by Tomek Korzeniewski · with Lwazi Mthembu, Plumber and drain specialist

Key takeaways

• A trap is due for cleaning when the fat and sludge together take up about a quarter of the trap.

What a grease trap does to the water leaving a kitchen

So you have a grease trap. Good. But here's the part most people miss.

A grease trap is a box that sits between your kitchen sinks and the main drain. Hot water from washing up carries fat, oil and food scraps down the pipe. When it hits the trap it slows down and cools.

The fat floats to the top while the heavy bits sink to the bottom. The cleaner water in the middle flows out to the sewer. The trap only works, he says, if it's big enough and if someone empties it.

The question that matters is not whether you have a trap. It's whether that trap suits what your kitchen cooks, because grease trap upkeep for restaurant kitchens depends on getting that sizing right from the start.

Sizing a trap to match the menu, not the floor plan

Two things decide the size of a trap. How much water comes out of the kitchen at peak and how long that water needs to sit in the trap to separate.

A small guest house doing breakfasts has one short busy spell each morning, with a lot of pans and plates. A restaurant doing lunch and dinner has two long busy spells, with fryers and grills. The restaurant needs a bigger trap, or even two, though the kitchen might look the same size.

So he counts the sinks when he sizes a trap. He checks for a dishwasher, looks at what they cook and asks how many covers they do on a busy night. Fried food means far more oil than a salad bar. The menu drives the size, not the measurements of the room. Size it that way once, then the trap only keeps working if the cooking stays the same.

The sizing mistakes that cause a trap to fail early

Get the size right once and you still have two ways to get it wrong. Someone buys a building that used to be a coffee shop, turns it into a burger place and keeps the old trap. The coffee shop made toast. The burger place runs two fryers.

That trap fills up in a couple of days. After that the fat sails straight through into the drain. The old size never stood a chance against the new menu.

The second mistake is a trap big enough for the job but sitting in the wrong place. His rule is blunt. If you can't get to it, it won't get cleaned.

Choosing a spot the trap can actually be reached

So reach is the deal. The best spot for a trap is outside if possible, close to the kitchen, with a lid you can lift without tools and room for a service vehicle to reach it.

He's honest that a lot of local properties fight you on this. In Kalk Bay and St James the buildings are old and they go straight onto the pavement. There's no easy outside spot to use.

When that happens, he finds the least bad place inside. Usually that's a back scullery, with a sealed lid so there's no smell in the kitchen. Reachable beats tidy. A trap you have to dismantle the kitchen to open is a trap that gets skipped. But getting to it is only half the job. Even an easy lid fills up if nobody minds what goes down the drain between visits.

The daily habit that stops fat reaching the drain

Keeping a trap working takes two parts and the first one is yours. Mthembu says kitchen staff should skim the top and check the baskets daily, or every few days depending on the trap. It's a five-minute job with gloves and a scoop.

The second part is the proper pump-out and clean. He empties the trap completely, scrapes the walls, checks the baffles and the outlet. Then he refills it with clean water so it works from the first wash. He also leaves a service sheet on the wall with the date and what he found.

His rule for timing is one you can check yourself. When the fat layer on top plus the sludge on the bottom takes up about a quarter of the trap, it's due. For a busy restaurant that might be weekly. A guest house doing breakfasts might only need it monthly. Over the first couple of months he measures it on every visit, then sets a schedule that fits that kitchen.

Warning signs a trap is already struggling

So what does Mthembu check first? Slow sinks in the kitchen. Then a smell, especially a sour one near the trap or the floor drains. Gurgling counts too. So does water coming up through the floor drain when the dishwasher empties.

Open the lid and look. If the fat layer is thick and solid, the trap is overdue.

Sometimes you open the lid and there's no fat at all. Yet the drain still blocks. That usually means the fat is going straight through, because the trap is too small or a baffle has broken. Staff can also work against the trap without meaning to. Pouring hot oil down the sink is the big one. It cools a few metres down the line and sets hard. Strong degreasers can break fat into tiny bits that pass the trap and set further down the drain, moving the problem somewhere harder to reach. Spotting the signs early is one thing. Knowing what a plumber actually does once that call comes in is another.

What happens once a blocked drain call comes in

The work starts the moment he arrives.

Then he puts the camera down to see what's left. He's seen drains where the pipe has shrunk to the size of a thumb, all of it fat stuck to the walls, the kind that sets like candle wax. The camera shows you the real state of the line, not a guess.

After the pipe is clear he cleans the trap properly and looks at why it failed. Is it too small? Has the menu changed? Is somebody pouring oil down the sink? He fixes the cause, not just the blockage, because grease trap upkeep for restaurant kitchens means sorting the reason, not patching the symptom. A blockage you only clear comes straight back.

Why Cape Town's older pipes make the job harder

A lot of the drains on the Main Road side in Muizenberg and Kalk Bay are old clay pipes. Over the years their joints have shifted.

Fat catches on every step in the pipe. It builds up faster. Roots find those shifted joints too. So a guest house in an old building needs its trap looked after even more carefully than a newer place. Mthembu would also suggest a camera check once a year, on the line from the kitchen to the street.

For a kitchen in one of these older buildings, the next step is a proper pump-out of the trap itself. Our grease trap cleaning handles that. We scrape the sides and walls. We also check the baffles are clear.

Ready when you are

If you would like to take this further, Grease trap cleaning is the place to start.

About the expert

Lwazi Mthembu, Plumber and drain specialist.

Frequently asked questions

Does a restaurant or café actually have to have a grease trap?

Most kitchens that cook on site need one under local by-laws, because the sewer can't cope with fat and food waste going in raw. If you're not sure your trap meets the rule, the city's health or engineering department is the place to check, not a guess.

How often should a busy kitchen's grease trap be cleaned?

There's no single answer, it depends on how much you cook and what you fry. A busy kitchen running fryers and grills fills a trap far faster than one doing toast and coffee, so the real test is watching how quickly the fat and sludge build up and setting a schedule around that.

What does keeping a grease trap maintained actually involve?

It's two jobs working together. Someone in your kitchen skims the top and checks the baskets every few days and separately the trap gets a full pump-out, scrape and baffle check on a schedule that matches your menu.

Will a plumber rush my job because they're already thinking about the next call-out?

A proper job on a trap or a drain means clearing the blockage, checking the cause and leaving a note of what was found, not just packing up the minute water flows again. If a job feels rushed, ask what caused the problem before you let anyone leave.

Could I get overcharged for something that turns out to be a simple fix?

A photo of the problem before anyone arrives lets you get a straight quote before any work starts, so there's no surprise once the job is done. Ask for that quote in writing before you agree to anything.

Will the plumber actually show up when they say they will?

A time that's been agreed should be kept and if something changes you should hear about it before the slot comes and goes. If a company can't give you a specific window, that's worth asking about upfront.

Could I end up with a big invoice for work that doesn't even sort out the problem?

That happens when only the blockage gets cleared and nobody looks at why it happened, so the same fat or root comes straight back. A proper visit checks the cause, whether that's a trap that's too small or a pipe that's damaged, so the invoice matches work that actually holds.

If I need paperwork for an insurance claim, will I get it sorted along with the repair?

Insurance paperwork is a separate conversation from the repair itself, so it's worth asking upfront whether a company can help with that side of things, rather than assuming it comes standard with every call-out.

What happens if I call and nobody picks up?

A missed call should get a call back the same day, not a voicemail nobody checks. If you're waiting on a drain or trap problem, a WhatsApp message with a photo is often a faster way to get a straight answer.

Why do big companies never seem to call you back when you need them?

A call centre often passes your message through several hands before it reaches someone who can actually answer it and each handover is a chance for it to get lost. A smaller outfit where the person who answers is the person who comes out tends to close that gap.

What if the plumber turns up without the right gear to sort my drain or trap?

Clearing a kitchen drain properly usually needs a jetter to shift the blockage and a camera to see what's really going on inside the pipe, not just a plunger and a guess. If the first visit doesn't fix it, ask whether the right equipment was actually used.

Who is responsible for looking after a grease trap, the owner or the tenant running the kitchen?

That's usually set out in the lease rather than by any general rule, so it's worth checking who's named as responsible before a trap gets neglected. Either way, the kitchen using it daily is the one that notices first when something's wrong.

About the author

From Klipspringer Plumbing

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