Purchase pure isopropyl. You can buy 99 percent isopropyl from most large drugstores; it is not a prescribed product so it is suitable for immediate purchase. You can also buy the product online.
Dilute seven parts isopropyl with three parts water. This is a common measure; "rubbing alcohol" has 70 percent isopropyl content.
Decide how much of the product you need. Remember to scale the measurements so that it is always seven parts isopropyl to three parts water.