After you use a plunger especially in a toilet you should wash the plunger off before storing it.
When I need to use a plunger I fill a bucket with some warm water and then add some bleach to the warm water in the bucket.
I then take the used plunger and allow it to sit in the bucket of bleach and water for 5 to 10 minutes.
Then I remove the plunger from the bucket and rinse the plunger off to remove the bleach and clean the plunger.
Then I place it in another bucket I keep in the bathroom closet until I need to use it.
Always keep separate plungers for the toilet and kitchen sink so that you do not cross contaminate your sink from the toilet.
I just rinse off the kitchen plunger as well and place it under my sink cabinet.
Washing off the plunger helps to get rid of germs so that you don't spread germs.