This is after putting Harpic Automatic Toilet Bowl Cleaner into the toilet bowl tank. When flushing, you can see that the bubbles created. There is a pretty strong fragrance as well. Pretty useful in my opinion.

The Harpic Automatic Toilet Bowl Cleaner in packaging: https://www.youtube.com/watch?v=7xKy-pXJYdA

Putting the Harpic tablet into the toilet bowl tank: https://www.youtube.com/watch?v=37o4TN7Bhng