What Happens to Used Cooking Oil When it Goes Down the Drain

Cooking oil is a staple within commercial kitchens. It’s required for deep frying, and the various types of cooking oil to choose from affect the taste and texture of the food.

Once a batch of restaurant cooking oil is spent and no longer good for frying, it must be disposed of somewhere. Because it is a liquid, you might be tempted to pour restaurant cooking grease down the drain, but that should never be an option. What might seem like an easy solution to dispose of waste, will only cause your business major problems, costing you time and money in the long run.

Here is a look at what happens when used cooking oil is poured down the drain and why your restaurant staff should never do it.

Grease on a table, before fully cooling with text in front of it saying "Grease hardens when it cools, meaning that it won’t remain a liquid for long. Once it hardens, it will stick to the side of your drainage pipes and residue will begin to build up."

1. Cooking Grease Hardens When it Cools

While your hot restaurant cooking oil might look no different than soapy water when it’s disposed of, it won’t remain in that state. Grease hardens when it cools, meaning that it won’t remain a liquid for long. Once it hardens, it will stick to the side of your drainage pipes and residue will begin to build up. Just like any other plumbing issue, residue collecting on the side of pipes will eventually build into a clog.

Your staff will likely remain unaware of this budding issue until it becomes just that – a major problem. As the grease buildup accumulates on the side of your pipes, it will catch food-related debris and whatever else goes down your drain, too. This will eventually cause a blockage and other plumbing problems within your grease trap, leaving you with an expensive problem to fix, and potentially a mess to clean up. It will also increase the fees associated with your grease trap service due to having to pump more frequently because of the used cooking oil getting into the trap.

You might think that chasing the spent cooking oil with water will help get it through the drainage pipes, but it will make little to no difference. Water doesn’t help it slide past. It’s not hot enough and no soap is strong enough to prevent oil from hardening, catching to the sides and causing a clog.

Plus, the amount of grease that does get through your drainage system doesn’t end up in a better place. In fact, the more that slips by will eventually become an even bigger and potentially more expensive headache.

2. Cooking Grease Will Enter the Sewage System

Even if some of the grease gets through your pipes without hardening, the sewer is often bigger and more serious issue. Sewers are full of chemicals from cleaning supplies, oxidized pipe systems and other various forms of decomposing waste. When grease is added into the mix, it becomes a large problem – figuratively and literally. When the grease comes into contact with these chemicals, they react together and form a new soapy, waxy substance that gets sticky and enlarges — sometimes referred to as a fatberg.

What is a fatberg?

A fatberg is the accumulation of oil and grease that's been poured down the drain, congealing around flushed nonbiological waste. Think of it as grease expanding like a bubble but building up like a snowball when it comes in contact with chemicals and other forms of waste found in the sewer.

Fatbergs can become very large and can harden to the level that feels similar to concrete. According to some estimates, fatbergs can grow to more than 800 feet long and weigh up to 100 tons. You may not have imagined something of that size forming just from cooking oil being poured down the drain like water, but it can easily become. They often require specialized equipment to remove. Once a fatberg forms and enlarges, it becomes a serious issue for the city’s sewer system. For example, clearing out grease fatbergs costs New York City nearly $4 million annually. Is pouring grease down the drain worth it?

3. Costly Fines, Environmental Harm

If a fatberg or other grease-related problem occurs in your municipality’s sewage system, and it is traced back to your restaurant pouring grease down the drain, you will be on the hook for a costly fine from your local municipality. For example, in Texas, a first violation penalty of $400, a second violation within two years the of first will result in a penalty of $500 and third violation within two years the of first will result in a penalty of $750. That doesn’t include potentially being on the hook for damage to the city’s sewage pipe system.

The environmental harm is real. Sewer floods and backwashes can deposit garbage and raw sewage into the surrounding area. This is toxic to plants and wildlife, as well as damaging to the local environment. No one wins when grease is poured down the drain. There is no upside to it and what might seem like a quick and easy discarding of waste will only cause your business problems in the end.

So, what should you do with your used cooking oil?

4. Recycle Used Cooking Oil with a Reputable Provider

Recycling with a reputable recycling partner is always the superior option when it comes to disposing of your used cooking oil. It not only serves as a preventative measure from plumbing issues, but it will also improve your bottom line and work to the benefit of the health of the environment in the long term.

That grease you are tempted to pour down the drain has value when placed in the right hands. A reputable service provider will pay a market-based rebate for your used cooking oil and provide regular service to your business. Why let money flow down the drain? Additionally, some grease recycling companies repurpose your used cooking oil into ingredients used in the production of renewable diesel – a cleaner burning alternative to petroleum that helps curb carbon emissions. As much as pouring oil down the drain is a lose-lose for all involved, recycling used cooking oil a win-win proposition.

No one wins when used cooking oil is poured down the drain. Make sure your business is safely and responsibly discarding your frying oil and that you are getting the consistent value out of a commodity that fries your delicious food and improves your bottom line when handled properly.