Make a paste out of baking soda and dish soap and scrub it thoroughly, then rinse with hydrogen peroxide and again with lots of hot water.

you might try airing it out in sunlight for a few days I have had success with that with a strong mold smell in a soft lunchbox that resisted washing.

I really hate when plastic tupperwares ooze grease even if you wash them ten times . If baking soda doesn’t work, there is an even stronger option: washing soda.

I use baking soda to wash holiday glassware that spends all year on top of the nasty cabinets above the stove and it kills the sticky mildew feel almost instantly. But when push comes to shove, washing soda is even more insane than baking soda.

Just be sure to rinse thoroughly so it doesn’t end up in the food

Plastics are notorious for catching smells and keeping smells.

I just replaced a plastic kitchen trash can with a metal one because of this.

I laughed to myself as I took the old one to put in the trash. I had never removed a sticker advertising “Traps Odors Inside!” That sticker wasn’t fucking kidding as this thing had sucked up every bad smell that had gone in the trash over two years. It “trapped” those odors all right, and every time I lifted the lid, they would come out to greet me.

As much as it sucks, the best solution would to be replace the lunchbox with a similarly sized metal one or fabric one (that can be washed).

make Indian food and leave it in there until it rots.

This is an out of the box idea (no pun intended), have you considered using an effervescent denture cleaner like Effordent? Fill container with warm water and dump a bunch of tablets in it.

I’d start with washing and letting it sit in the sun a couple of days. If that doesn’t work I’d go nuclear with an ozone generator just be easy with it or it will turn the food smell into an off-gasing plastic smell, and don’t use it in an occupied space. Idealy stick it in a tote outside or something like that.

Napalm

Once I had a non stick frying pan catch the smell of laundry detergent pods and the stuff wouldn’t go away, ruining my breakfast. Vinegar didn’t work. So I cooked oats and oil until burning it almost. That removed the smell. I know it’s different with a plastic container as you can’t put it on the stove, but I would try storing and reheating some very oily porridge in that container. Sometimes what detergents and acids can’t remove, oils wipe awat easily. But, do try the vinegar first.

Dunk it in vinegar overnight. It will kill bacterias, and the smell of vinegar itself will go away pretty quickly.