Fish smell lives in the plastic, not on it.

Fish and curry odors soak into the plastic itself, so scrubbing won’t fix it. You need a soak, not a scrub.

Plastic lunch boxes are slightly porous, and smell molecules lodge in micro-pores that dish soap can’t reach. The fix: a few tablespoons of baking soda dissolved in warm water, and let the box soak for a few hours — overnight if it’s bad. Baking soda neutralizes the acids causing the smell. Don’t bother with the baking soda + vinegar trick; they just cancel each other out in a fizzy nothing.

After the soak, wash normally, then leave the box in direct sun for a couple of hours. That step sounds like granola nonsense, but it’s the most effective one: UV light kills the bacteria behind the smell and breaks down odor molecules better than any kitchen cleaner.

If it still stinks after that, the plastic is done — pitch it and get a glass container for curry nights. Some cheap boxes never come back.