The highest enchantment for anything is a level 30. Level 30 enchantments are usually very high and very good.
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Actually you don't need more than 20. Minecraft enchanting is all luck, you can actually get every natural enchantment on a pickaxe with level 25.
I do not know why you would want to clear your XP, but if you do, kill yourself In-Game.
/ xp /kill /me / gamemode 1 those are the useful ones
Use Iron Ingots on an Anvil in Minecrafft 1.4+. (It requires XP)
By xp bottle you mean bottle o'enchanting. They cannot be made, but can be aquired by trading with a priest villager or spawning one in by creative mode or cheats.