Nothing is nastier than finding an old, crusty sippy cup with the makings of cottage cheese in them. If you can get past the rotting smell, the sippy cup can be cleaned and used another day. Sippy cup lids are notoriously hard to clean because of the valves and crevices. Follow these steps to clean your sippy cup lids the right way every time.
Remove the valve and wash the entire lid with dish soap. Using a bottle brush with a lid cleaning attachment is your best bet. You can find these brushes in the baby department of major retailers or grocery stores. Clean the lid with the large part of the brush and then use the small lid cleaning attachment to get the crevices clean. If the small brush is not working, try using a cotton swab or a pipe cleaner. These items are perfect for the small crevices.
If the above step did not work, put the entire lid and valve on the top rack of the dishwasher. Place the smaller parts in a baby bottle basket or mesh bag to make certain that they are not lost in the dishwasher. You can find either of these items also in the baby section of a major retailer or grocery store. Using the top rack gets the parts clean but does not expose them to the full blast of the bottom rack.
Try the boiling method. This method will sanitize the lids and valves while removing any buildup. Put two cups of white vinegar into a pot of water. Drop the sippy cups lids into the boiling water and let them boil for 6 to 8 minutes. Remove and let cool on a dishtowel. Then wash everything with soap and water to remove the smell.
Get out the Polident and no, it is not for your dentures. Put one Polident tab in a bowl of water for every two sippy cup lids and valves. Follow the Polident directions and drop everything in. Once you have finished, remove everything and wash immediately with soap and water to remove the smell.
Try a baby bottle microwave sterilization bag if nothing else has worked. Place all of the items that you wish to clean in the bag and put the appropriate amount of water in the bag as well. Place the bag into the microwave and follow the steaming directions. The steam often will work and remove any left over items that the previous methods could not remove. By this point, all bacteria, mold and food should be removed from the sippy cup lid. If not, throw everything away.