Food-container lids can retain sauce and moisture in places that are easy to miss. The broad top may look clean while a gasket channel or clip hinge still contains residue. Make a quick inspection part of washing up, especially after oily foods or sauces.
Check the manufacturer's instructions before taking the lid apart. Remove a gasket only if it is designed to be removed, and note how it fits before washing. Do not pry out bonded seals or dismantle a valve without instructions explaining how to reassemble it correctly.
Wash the components using the approved method. Dishwasher suitability may differ between the lid and base, and some parts may need a particular rack position. Hand washing is not a license to use harsh abrasives or very hot water on a material that cannot tolerate them.
Give small spaces attention
A suitable soft brush can help clean a groove when the manufacturer permits it. Work around the whole seal rather than focusing only on visible food. Rinse away detergent thoroughly and inspect the parts in good light.
Check for cracks, tears, warping and changes in how the lid closes. A clean but damaged gasket may no longer seal properly. If replacements are available, match the exact model or part number; a similar-looking ring can fit badly.
Dry the lid and any removable components separately where air can reach them. A towel may remove surface water, but moisture can remain in a recess. Avoid closing the empty container while its seal channel is still wet.
Once everything is dry, reassemble the lid as directed and check that the gasket sits evenly. Keep the lid with a compatible base or in a clear storage group so that you do not force it onto the wrong container later.
Make the next wash easier
Empty leftovers and clean the box promptly after use when possible. Leaving food to dry hard in the lid can make cleaning slower and less thorough. If you must transport an empty lunch box home, wash it fully when you return rather than treating a quick rinse as complete cleaning.
A simpler lid may be worth choosing when several elaborate closures have become a washing burden. Easy access to every food-contact surface is a useful feature in its own right.