I had a container that had held curry once, months ago. It had been through the dishwasher a dozen times since. It still smelled like curry, and so did anything I put in it.
Two of these actually fix it, and the rest are the ones people repeat online without testing.
Why Plastic Holds Smells and Glass Does Not
Plastic is porous at a microscopic level, and the molecules that carry smell are oils. Those oils soak into the surface, so they are not sitting on the plastic where soap can reach them — they are in it.
Detergent and water cannot pull out something that is absorbed. That is why the dishwasher does nothing, however many times you run it.
To get a smell out you either have to draw the oil back out or neutralize it in place.
What Works
Baking soda paste, left overnight. Two tablespoons of baking soda with just enough water to make a thick paste. Coat the inside, put the lid on loosely, leave it twelve hours, then wash normally.
Baking soda is alkaline and most food smells are acidic, so it neutralizes rather than masks. Leaving it on is the part people skip — a quick scrub does not work.
Crumpled newspaper, three days. Stuff the dry container with newspaper, seal the lid, put it in a cabinet and forget it. This is the one that sounds like nonsense and works better than anything else.
Newsprint and its ink are extremely absorbent and they pull the oils out of the plastic into the paper. For a bad container this beats baking soda.
Sunlight. Wash it, then leave it open outside in direct sun for a day. UV breaks down the smell compounds. Works well and costs nothing.
What Does Not Work
More dishwasher cycles. The smell is not on the surface.
Bleach. It kills bacteria, which is a different problem, and leaves plastic smelling of bleach instead.
Vanilla extract or coffee grounds. These replace one smell with another. The curry is still there underneath and in a week you will have both.
Freezing it. The smell comes back with the temperature.
How to Stop It Happening
Rinse in cold water first, before hot. Hot water opens the plastic and drives the oils in. Cold rinses the fat off the surface before that can happen.
Wash it the same day. A container left with curry in it for two days is a much harder job than one rinsed straight away.
Keep two or three containers for the strong stuff — curry, chili, garlic, fish — and let them smell however they like.
Use glass for leftovers you will reheat. Glass is not porous, so it never takes a smell at all, and it does not stain from tomato either.
Start With the Worst One
Take the container you were about to throw out and fill it with newspaper tonight.
Three days is nothing to get it back.
