How to remove tea scale from double-layer stainless steel thermos cup

To remove tea scale from a double-layer stainless steel thermos cup, the following methods can be used:

Use water and detergent: Pour warm water into the cup, add a small amount of detergent, gently scrub the inner wall of the cup with a brush, focus on cleaning the area where tea grime accumulates, and then rinse with clean water.
Lemon juice and salt: Cut the lemon into slices, place in a cup, sprinkle with some salt, gently rub with your hands to mix the lemon juice and salt, let the mixture in the cup sit for a while, then rinse off with water.
Vinegar and baking soda: Mix a certain percentage of vinegar and baking soda, apply to the inside of the cup, gently scrub with a brush, and rinse off with clean water.
Bleach: Pour water into a cup, add a small amount of bleach, let the bleach solution in the cup sit for a while, then rinse off with clean water. Note: Dilute bleach according to product instructions and use safety gloves.
White vinegar soaking method: Add an appropriate amount of white vinegar to the cup, then add water, soak for about an hour, and gently wipe with a soft cloth or sponge.
Baking soda method: Add an appropriate amount of baking soda to a cup, then add warm water and wipe with a soft cloth or sponge.
Toothpaste method: Squeeze an appropriate amount of toothpaste into a cup, then add warm water and wipe with a soft cloth or sponge.
Lemon juice method: Apply lemon juice to the tea stain area, wait a few minutes, and wipe with a soft cloth or sponge.
Regardless of which method you use, be sure to rinse it thoroughly with clean water to avoid the effects of residue on human health. Stainless steel cups should be cleaned frequently to prevent excessive tea dirt from breeding bacteria.