That instinct to drop anything plastic, paper or cardboard into the recycling bin is hard to shake, but it’s also one of the biggest reasons recycling programs struggle. A single grease-stained pizza box, black plastic clamshell or unrinsed yogurt cup can throw off the sorting process at recycling facilities, and the result isn’t just a few items being pulled aside. In many cases, contamination leads to entire truckloads of recyclables getting rerouted to the landfill.

Jeremy Walters is a sustainability ambassador for Republic Services, one of the nation’s largest recycling companies. He’s seen the effects of wish-cycling firsthand. Walters walked me through the most common mistakes people make when recycling food-service packaging, bags and containers at home — and what to do instead.

Below, you’ll find his tips for recycling and a list of containers that can and cannot be recycled at most facilities. 

How to properly recycle takeout containers

1. Do some recycling research: The most important thing you can do to streamline the process is find out which containers can and can’t be recycled in your area. Depending on where you live, this will likely vary, so you’ll need to check with your local sanitation department, often via its website. 

2. Don’t assume it can be recycled: Just because a takeout container has a recycling symbol on it doesn’t mean it can be recycled where you live. Some cheaper producers of takeout containers will label items as recyclable even if they’re not.

3. Give ’em a good rinse: When recycling takeout containers, ensure they’re as clean as possible. Residual food waste, especially grease, can make a material unrecyclable. 

What follows are general rules and guidelines on which takeout containers can and can’t be recycled, as well as how to recycle them effectively.

Read more: Some Blue Apron Meal Kits Are Cheaper Than Buying the Groceries

7 takeout containers that can’t be recycled

1. Polystyrene foam containers, often referred to as “Styrofoam,” are widely used for takeout and delivery, so you’ve likely seen them. Unfortunately, they aren’t recyclable and must be thrown out.
2. Black plastic containers: These are another popular choice for restaurants and while they are often made from recycled materials — making them at least somewhat eco-friendly — they can’t be recycled and must be tossed. According to Walters, recycling plant sorting technology hasn’t yet kept pace with these materials.
3. Chinese containers and clamshells: This is another type of container that could, in theory, be recycled, but because oil often seeps into the cardboard, you’re better off throwing it away. Also, many are coated with a sealant, making them leak-proof and difficult to recycle.
4. Oil-stained pizza boxes: Theoretically, corrugated cardboard can be recycled but not when it’s soaked in oil or caked with cheese. Happy medium: Take the top portion of the box if it’s free from petroleum and recycle that with your cardboard. The bottom half will likely need to be trashed. 
5. Plastic bags: Your food is often delivered in plastic bags, but they aren’t recyclable and can cause harm to your local recycling facilities. To dispose of plastic bags, return them to the store where you got them or reuse them. Better yet, don’t use them at all; instead, request a paper bag.
6. Plastic utensils: Not everything made from plastic is recyclable, and the recycling of plastic utensils typically depends on your local facility. Therefore, check with your service provider for details. Even better, when you place your order, let the restaurant know you don’t need plastic utensils.
7. Soiled paper plates and napkins: These items are not recyclable when soiled with food and liquid, so look for reusable, biodegradable or authentic disposable products instead.

Some cities, such as Austin, Texas, have curbside composting for food-soiled paper products. A program like this may not be available in your community but it doesn’t hurt to check. And Block Bins, a shared-bin composting startup launched in Chicago, provides a similar service even if your town or city doesn’t. 

Read more: Microwave-Free Zone: Expert Hacks for Reheating Leftovers 

5 takeout containers that can be recycled

1. Plastic clamshell containers: Clear plastic takeout containers with a recycling symbol can be recycled. If it’s a plastic container labeled No. 1 or No. 2, you can recycle it and should whenever possible. 
2. Aluminum containers: You know the ones you can never close as tightly as the restaurant did the first time, no matter how much you pinch? Yeah, those are recyclable as long as they’re clean.
3. Paper or cardboard containers: These are often made from recycled materials and can be recycled themselves. Some are biodegradable and compostable, as long as they are thoroughly cleaned and haven’t absorbed much grease. Even ones that aren’t recyclable are far less toxic than plastic or Styrofoam when being processed, burned or buried. 
4. Paper bags: Many restaurants send their orders in large paper bags and those absolutely can and should be recycled or reused. Plastic bags, on the other hand, can’t be.
5. Clean paper products: Paper plates, napkins, and cardboard pizza boxes that are not heavily soiled with grease can generally be recycled.

What else can you do to help?

If you feel comfortable gently letting your local restaurant know you’d appreciate them using one of the many environmentally friendly alternatives to plastic and polystyrene, you should. You could also send a polite, anonymous email expressing your appreciation for the food and service, but with one small request on behalf of the Earth. 

For more green stuff, check out our list of the most environmentally friendly meal kits and learn how to properly recycle metal cans. Yes, pizza boxes can be recycled — but only the parts without grease.Wishful thinking won’t make these items fit for the blue bin.