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If the residue goes all the way to the top of the pot, fill the water to about an inch below the top. Stainless steel fondue pots are usually stovetop safe, but check the safety directions before putting it on the stove. Some stainless steel pots have glass or ceramic inserts that cannot be heated on a stove. You'll be pouring the water back into your fondue pot, so make sure the separate pot isn't too big and that you can easily pour from it. The amount of time this takes will depend on the amount of water, the thickness of your pot, and how high you turn up your stove. Keep an eye on your water to make sure it doesn't boil over. Use an oven mitt or pot holder to protect your hands from the hot metal. Pour slowly so you don't splash yourself with the scalding water.
Fill the fondue pot with water to the level of the residue. Place the pot on the stove if it's stovetop-safe. Pour the water into a separate pot or kettle if it's not stovetop-safe. Heat the water until it starts boiling and remove it from the stove. Pour the hot water into the fondue pot if you heated it separately.