What Not to Do with Used Cooking Oil (And Smarter Ways to Handle It)

If you cook at home, you’ve probably faced this question at least once: how to dispose of used cooking oil? It’s easy to ignore, but improper disposal can lead to real problems—clogged pipes, environmental damage, and even unexpected costs down the line. You might think pouring it down the sink with hot water will flush it away, but that’s a recipe for disaster. Tossing it in the trash without sealing it? That just makes for a greasy mess.

Disposing of used cooking oil the right way isn’t complicated, but plenty of people get it wrong. In this guide, I’ll break down the worst mistakes people make, why they matter, and the smarter, cleaner ways to handle used oil.

Why You Should Never Pour Cooking Oil Down the Drain

David Badger, a project manager at Pima County’s wastewater department, has seen just how much damage cooking oil can cause. “People think because it’s a liquid, it’ll just wash away,” he says. “But once it cools, it hardens in pipes and sticks to everything inside.” Over time, that buildup leads to massive clogs, which can cause sewer backups—not just in your home but in entire city pipelines.

It doesn’t stop there. Once oil gets into the sewer system, it mixes with other waste and debris and creates what’s known as a fatberg. These giant, greasy masses clog pipes so badly that cities spend millions removing them. In extreme cases, sewage can back up into homes or overflow into streets, leading to major health hazards.

And if you’re thinking a little oil won’t hurt? Think again. Even small amounts add up. That’s why plumbers and city officials alike recommend never, ever pouring it down the drain—even if you follow it with hot water or soap. 

Can You Reuse Cooking Oil? Here’s When to Keep It and When to Toss It

Reusing oil isn’t just a cost-saving trick—it’s completely fine if you do it the right way. But there’s a limit. Every time oil is heated, it breaks down a little, and eventually, it reaches a point where it’s no good. The trick is knowing when it’s still safe to use and when it’s time to get rid of it.

If the oil looks relatively clear, smells normal, and hasn’t been used to fry strong-flavored foods (like fish), you can strain it through a fine mesh or cheesecloth and store it for another round. Keep it in a sealed container, away from heat and light, and it should last for several more uses.

On the other hand, if your oil is dark, thick, has a burnt smell, or smokes excessively when reheated, it’s done. Using old, degraded oil doesn’t just affect taste—it can release harmful compounds that aren’t great for your health. When in doubt, toss it.

How to Dispose of Used Cooking Oil

So, if pouring it down the drain is a bad idea and reusing it isn’t always an option, what should you do instead? Here are a few simple, clean, and safe ways to dispose of it:

Store and Discard Properly

Let the oil cool completely, pour it into a sealable, non-breakable container (like a coffee can or an empty plastic bottle), and throw it in the trash.

Mix with Absorbent Materials

If you only have a small amount, mix it with something like cat litter, coffee grounds, or flour to solidify it before tossing it. This keeps it from leaking and making a mess.

Drop It off at a Recycling Center

Many cities have collection sites where you can take used oil to be turned into biodiesel or other eco-friendly products.

Check for Local Collection Events

Some communities hold special events where residents can drop off used oil after major cooking holidays, like Thanksgiving.

No matter which option you choose, the key is keeping oil contained so it doesn’t leak into the environment or cause plumbing problems.

Can You Recycle Cooking Oil? (Yes, and Here’s How!)

Believe it or not, cooking oil isn’t just waste—it can actually be repurposed. Many recycling centers turn used oil into biodiesel, a cleaner-burning alternative to petroleum diesel. Mike Kazz, president of Grease Cycle, explains why this is a better option than simply throwing oil away: “Used cooking oil actually has value. Instead of clogging drains, it can be refined into biodiesel, which is 80% cleaner than petroleum-based diesel.”

Recycling oil is fairly easy if your city has the right programs. The process usually involves collecting the oil in a sealable container and dropping it off at a designated recycling center. Some places even have collection bins at grocery stores or gas stations, making it even more convenient.

The key to recycling is keeping your oil as clean as possible. Water, food scraps, and excessive debris can make it harder to process, so always strain out solids before storing it. If you’re not sure where to take it, check your city’s waste management website or call your local recycling center.

Creative Ways to Repurpose Used Cooking Oil

If you’d rather put your used oil to good use around the house, there are plenty of creative ways to repurpose it. For example, some people make homemade candles or soap using filtered oil as a base. It’s also great for lubricating squeaky hinges, gardening tools, or even bike chains.

You can also use used cooking oil to make bird feeders. Mixing cooled oil with birdseed creates suet cakes, which provide extra energy for birds during the winter. If you have wooden furniture or cutting boards that need some TLC, a small amount of vegetable oil can help restore shine and protect the surface.

Just remember—if the oil smells rancid or has been used too many times, it’s best to dispose of it properly rather than repurpose it. Once oil degrades, it’s no longer safe to use in any capacity.