I run mine through the dishwasher make sure it is secure in top shelf. I wedge it between other items. Also sometimes I add water and dish soap and place in microwave for 1 minute or 45 seconds as the media has reported this to sterilize it.
Check the correct time my time is an estimate. The dishwasher works great.
Kitchen sponges are awful harborers of bacteria. The only way to safely use them is to wash them in your washer every day just like you would a dish cloth.
Make a container of soapy bleach-water or soapy vinegar-water. Soak the sponge between uses, or at least one time per day. Wring out the sponge before use. Both kill bacteria that would otherwise live in the sponge. Allow the sponge to dry completely out at night. It may be best to alternate between two sponges, using the first one day and then the second the next day, and so on.
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How do you keep your kitchen sponge from smelling bad in between uses? I have done the microwave thing, where you put it in there for a few seconds...