Place 8 cups of water and the tea bag into the liner of the Instant Pot. (If using sugar, it can be added now and stirred until dissolved or added later.)
Close the lid, set the valve to the sealing position, and use the manual (pressure cook) button to adjust the time to 4 minutes.
After the time is up, allow a natural release for 15 minutes, then carefully remove the lid. *The contents will likely still be boiling and will definitely be hot and steaming.
Remove the tea bag using a slotted spoon. If you didn't add sugar before brewing the tea, it can be added now.
Allow the tea to cool to room temperature, add ice, or carefully transfer to a heat-safe container and move to the refrigerator to cool.
Serve cold and garnish with lemon if desired! Tea is good for 2-3 days when kept in a container with a lid in the refrigerator.
*The calories listed are an approximate and based on the ingredients and serving size listed. Sugar is optional and not calculated as part of the calories.*Recipe makes approximately 1/2 gallon of iced tea (8 servings).*Please see post for additional instructions, notes, and variations of the recipe.