The first thing you will have to do is to hack into the bottle. The Swiffer solution bottle is designed to be used once and then thrown away, ergo you must purchase another bottle to refill the solution. It is actually very easy to do, you simply boil a pot of water and turn off the heat, hold the cap part of the bottle in the water for 10-20 seconds to soften the plastic. Then you will be able to twist off the cap and use fingernail clippers or small scissors to clip off the locking tabs under the cap. Voila, now you can refill the bottle and reuse it as usual!
You can actually refill the solution with a couple of different things. You can use a mixture of 1 part PineSol (or any other concentrated cleaning liquid) to 3 parts water; or 1 part amonia, 1 part vinegar, 4 parts water.