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After you pop it open, check to make sure there are no remnants of food left inside. Give the container a quick preliminary rinse with hot water. Drain and shake out the excess water and place the container on the kitchen counter. If there's any dried or sticky residue inside the container, it may help to wipe it out with a paper towel before you begin cleaning. For best results, use pure distilled white vinegar. If most of the stains are concentrate around the bottom, you'll only need to add in an inch or two; if they reach up the sides, fill it to the top. Place the lid back on the container to keep the vinegar from spilling. Vinegar is strong enough to make an effective cleaner and disinfectant, but not so strong that it needs to be cut it with water. If you don't happen to have any vinegar handy, try using a little diluted rubbing alcohol or hand sanitizer. The alcohol in these products will produce an effect similar to the vinegar. As it soaks, the acidity of the vinegar will help break down any discoloration present while neutralizing persistent odors. It will also help clear away hard water deposits from previous washings. For heavier messes, you can leave the vinegar in the container for an hour or longer before cleaning it out by hand. Vinegar is naturally antimicrobial, which makes it useful for killing the bacteria that's had time to begin growing on old food. Adding a squeeze of fresh lemon juice can help brighten dull, discolored plastic and leave it smelling more pleasant. Once half an hour has elapsed, lift the lid and pour out the vinegar. Then, squirt a few drops of liquid dish detergent into the container and go over the inside using a kitchen sponge or stiff-bristled nylon dish brush. The rough surface of the scrubber should be enough to deal with any remaining stains. You may not be able to erase certain stains (like the infamous tomato sauce) entirely. Once these have set up in the plastic, it can be nearly impossible to get them out. Avoid scouring the container with anything more abrasive than a sponge. A device like steel wool or pumice stone may leave behind scratches in the plastic.
Remove the lid from the container. Fill the container with vinegar. Let the vinegar soak for 30 minutes. Scrub the container vigorously.