Isopropanol is Isopropyl Alcohol, also known as rubbing alcohol. Usually bought in drugstores or even grocery stores. WalMart sells it for about 2$ per quart, give or take, in 70% and 91% varieties. (The rest is water) It's available in my local market for slightly higher prices. Denatured alcohol is usually Ethanol (grain alcohol) with additives to make it poisonous. Sometimes Methanol is used for the denaturing. Methanol is wood alcohol and is poisonous. I have used Isopropyl to thin epoxy and have never had problems curing. I add only a few drops of alcohol per ounce of epoxy(10 or 15) and it thins nicely. I don't know but would assume the water evaporates when the epoxy cures as it gets hot. Generally when fuelproofing the tank compartment or engine bay I used Polyester resin. It's somewhat thinner than epoxy.