Easy as boiling water. I use a stainless Steel pot with matching lid. Any size will work. The bigger, the more char you can make. No need to vent. Put in as much cloth as it will hold, or as much as you want. Put the pot on your "out side" heat source, with the lid on. The gasses will start escaping around the lid. Once started, you may want to reduce heat some what. So long as you have a steady amount of gasses escaping, you're good to go. When it subsides, turn off or remove from heat. The residue around the rim will solidify and seal the lid on the pot, making it air tight. Let cool and you're done. I like to use thick Egyptian looped bath towels.