Soak it, don't just scrub it.

Soaking a smelly plastic lunch box in a hot vinegar or baking soda solution gets the odor out better than any sponge ever will.

Scrubbing only gets the surface. The smell is soaked into the plastic’s pores — especially if it’s a cheap container or it sat in a hot car. Soap won’t cut it.

Here’s what works: fill the box with hot water (as hot as tap gets), add a good splash of white vinegar or a couple tablespoons of baking soda, and let it sit for 30 minutes to an hour. Then wash normally. Vinegar neutralizes alkaline smells; baking soda handles acidic ones. If you don’t know which you’re dealing with, vinegar covers most food odors.

Sunlight is the secret weapon. After the soak and a normal wash, set the box in direct sun for a few hours. UV light and heat kill the bacteria that cause the lingering smell in the first place.

One caveat: if the plastic is heavily scratched or warped, no soak will save it. The smell is living in the scratches. That box is done — recycle it and get a glass one.