Gather your supplies. An old pot to boil water in, your empty Swiffer WetJet bottle, and your favorite cleaning solution.
Take the labels off the bottle.
Boil the water, and then put the bottle in the water for about a minute. The bottle will start to expand.
Pull the bottle out and use something to protect against burning your fingers. I used my shirt, but it may be better to use oven mitts. Twist the cap off while the plastic is soft.
Now so you can keep reusing this bottle, cut down the tabs inside the cap. I used scissors.
The cap will come off, but will still hold onto the bottle because we didn't mess with the thread.
Pour your favorite cleaning solution into the bottle at your own known measurements.
Mix with water. Now if you are afraid this might gunk up your Swiffer to use regular tap water, use Distilled water instead.
Place the cap back on snugly!
Replace the WetJet bottle into your Swiffer Enjoy your clean floors at a fraction of the cost.