A Plumber’s Simple Trick to Dispose of Used Frying Oil with Cornflour (Maizena)

If you do a lot of frying or you’re fond of deep-fried food, you’ll recognise the pattern: at some point the sink starts draining sluggishly, it gurgles, there’s a sharp smell - and in the worst case you end up needing an emergency call-out. That’s exactly where the story begins: a tradesperson uses the situation to show his customer a simple but highly effective trick. With an unremarkable powder from the kitchen, you can dispose of used frying oil safely - without wrecking your drain, your pipework or the environment.

How frying oil can ruin your drain

From the perspective of many home cooks, it seems perfectly sensible: let the oil from frying or deep-frying cool briefly, pour it down the sink, chase it with plenty of hot water - and job done. In practice, something very different happens inside the pipes.

At first, the warm liquid slips through the waste pipe without any trouble. But as soon as it meets cooler water and the relatively cold pipe wall, it starts to solidify. A greasy layer forms, clings to the inside, thickens, and gradually narrows the flow of the pipe.

On top of that, food scraps from the sink get involved: crumbs, pasta, bits of vegetables, leftover egg white. All of it sticks to the fatty coating. With every new dose of oil, the plug grows - until the water can’t get through at all. At that stage, professional equipment is often the only solution.

"Already a few millilitres of frying oil per wash-up are enough to gum up pipes over time and trigger costly call-outs."

Typical warning signs in the kitchen

Before a pipe becomes completely blocked, the drain tends to give clear signals:

• Water drains noticeably more slowly than it used to.
• The sink gurgles as it empties.
• A rancid or greasy smell rises from the drain.
• Sometimes water briefly pools in the bowl before it disappears again.

If you ignore these signs and keep tipping oil into the pipe, you risk a backup that eventually spills into the kitchen or bathroom - along with a foul smell and slippery residues.

Hidden danger in the sewers: fatbergs and environmental damage

The issue doesn’t stop at your front door. What starts in a domestic drain carries on into the public sewer network. There, fats from countless homes meet and merge into huge lumps. Engineers refer to these as fatbergs because some can weigh hundreds of kilograms and block entire sections of pipe.

These masses don’t just burden the sewer system; they also make the work of wastewater treatment plants harder. Removing fats from wastewater takes considerable effort. If some of it reaches rivers or lakes, it can form a film on the surface that disrupts oxygen exchange and harms wildlife.

"Every litre of cooking oil that ends up in the toilet or the sink worsens wastewater quality and increases operating costs for water providers."

The plumber’s tip: bind cooking oil with cornflour

Rather than lecturing, the plumber shows his customer a surprisingly straightforward alternative. His helper is a powder most people have tucked away in a cupboard - cornflour (corn starch), often known by the brand name Maizena.

Why cornflour works so well

Cornflour has a useful ability to bind fats and liquids. In sauces it thickens; with used frying oil it helps the contents set. That turns the liquid into a compact, comparatively dry mixture that can be disposed of in your general waste.

The approach is simple and only requires a little time:

1. After deep-frying, leave the oil in the pan or fryer to cool for a few minutes until it is only lukewarm.
2. Carefully pour the liquid into a heat-resistant container.
3. Add 1–2 tablespoons of cornflour per roughly 0.5 litre of oil.
4. Stir slowly with a spoon or whisk until no lumps remain.
5. Leave the container standing at room temperature.

Within around 24 hours, the oil-and-cornflour mixture turns into a thick, semi-solid mass. You can then scoop it out with a spoon, put it into a bag or an old carton, and throw it away with your general rubbish. Nothing leaks in the bin - and not a drop goes into the pipework.

What to do with larger amounts of frying oil?

If you only make chips or schnitzel occasionally, the cornflour method is a good fit. In households that deep-fry regularly, or where a large fryer is used, several litres can build up quickly. In those cases, other options tend to work better.

Taking it to the recycling centre or collection points

Many local authorities accept used cooking oil at the recycling centre. The liquid is collected in dedicated containers and processed further, for example into biofuel or industrial fats. If you’re unsure, check with your council or local waste contractor to see whether - and how - this service is available where you live.

Practical pointers:

• Decant old oil into tightly sealed bottles or jerrycans.
• Label the container clearly so it can’t be mistaken for anything else.
• Do not mix in harsh chemicals or cleaning products.
• Store the container in a cool, dark place until you can take it to a collection point.

That way, what looks like a messy waste issue can become a valuable raw material kept within a circular system.

Other mistakes that strain kitchen drains

Frying oil isn’t the only cause of trouble. Other habits also put pressure on the waste pipe and encourage blockages. Many happen simply through lack of awareness - and are easy to change.

Problematic item	What it does in the drain
Coffee grounds	Settles like sand in bends and traps
Rice, pasta	Swells in water and narrows the pipe
Flour, leftover batter/dough	Sticks with fat into hard lumps
Wet wipes	Do not break down and form cohesive clumps
Leftover paint, varnish	Adheres to pipe walls and is toxic to the environment

Using a strainer in the sink and disposing of waste thoughtfully via the bin prevents many problems before they start.

Why this trick saves money over time

A visit from a specialist can easily run into three figures, especially in the evening or at the weekend. If you need the drain cleared several times a year, you can end up spending amounts that would comfortably buy new kitchen appliances. By contrast, the method above costs only a few spoonfuls of cornflour and a bit of patience.

"A packet of cornflour costs only a few pounds. A single blocked pipe exceeds that amount many times over."

There’s also the day-to-day benefit: disposing of fats in a controlled way greatly reduces the chance of disrupted drains, unpleasant smells and kitchen chaos.

Practical add-ons for everyday life

Alongside binding oil with cornflour, a few routines are easy to build into normal kitchen life:

• After using frying oil several times, replace it fully and dispose of it in one go, rather than pouring small amounts down the drain.
• Once pan fat has cooled, wipe it out of the pan or pot with kitchen roll and throw the paper away.
• Once a week, run some hot water (not boiling water) with a squirt of washing-up liquid down the drain to help loosen fresh fatty residues.

If you deep-fry often, it can help to set aside a small spot in a cupboard for empty bottles or jars to collect used oil. That way, not a drop ends up where it doesn’t belong.

Risks, limits and sensible combinations

The cornflour method is not a substitute for proper disposal when you’re dealing with very large quantities. Nobody should be trying to handle several litres at once without a recycling-centre option in mind. It’s also essential that the oil has genuinely cooled before you mix it: oil that’s too hot can spit and cause burns.

If there are children in the home, keep containers of cooling oil well out of reach, and don’t use drinks bottles to avoid dangerous mix-ups. If you rent, it’s worth a quick check of any building rules, as some managing agents provide specific guidance on handling food waste and fats.

Combined with a sink strainer, occasional cleaning routines and taking larger amounts to the recycling centre, you end up with a robust system: pipes stay clear, the home stays largely odour-free, and the environment is significantly less burdened - all thanks to a plumber who spoke plainly once and then produced the right trick at the right moment.