This happened to me recently. I was using my "Swiffer WetJet" to clean my floor, and I ran out of the cleaning solution in the bottle. If you use a "WetJet" mop to clean your floors, you know that the bottle of cleaner that comes with the mop is impossible to open. I found a video that shows how you can refill the hard-to-open cleaner bottles with your own cleaning solution. It's a great way to save money and use the cleaning solution of your choice. 

Bonus: Never buy the expensive cleaning pads again. Here's a way to make your own.