Take the seal out. Vinegar soak. Done.

The rubber seal in a leakproof lunch box comes out, so pop it out and soak it in white vinegar.

That’s really the whole trick. Most people wipe the seal in place with a sponge and never get the mold out because it’s living in the crease where the seal meets the groove in the lid. Pull the seal free first — it should just peel out — then you can actually get at the stuff.

Mix white vinegar and hot water 50/50, or if you’re lazy, just pour straight vinegar in a bowl and drop the seal in. Leave it for 15 to 30 minutes. Scrub with an old toothbrush, paying extra attention to the folded edges, then rinse and dry it completely. Bleach works too but it’s hard on rubber, so treat vinegar as the first move.

The part everyone skips: moisture. Mold comes right back if you snap the lid shut while the seal is still damp. Dry the seal and the groove in the lid before you reassemble. If you’re storing the box empty, leave the lid ajar or prop the seal out until it’s fully dry.

Mold comes back if you store it wet, so dry the seal before you click the lid shut.