To avoid a metallic taste in your stainless steel water bottle, it's important to clean it regularly. 

How often you should clean your insulated water bottle will depend on how frequently you use it and what you use it for.

As a general rule, you should clean your sport water bottle after each use. This is especially important if you use it to store beverages other than water, such as juice or sports drinks, as these can leave residue and create an environment for bacteria to grow.

1. To clean your coffee mug, you can use warm, soapy water and a bottle brush to scrub the inside. 

2. You can also use a mixture of vinegar and water or baking soda and water to remove any stubborn stains or odors. 

3. Be sure to rinse your stainless steel tumbler thoroughly after cleaning to remove any remaining soap or cleaning solution.

4. If you notice a metallic taste in your vacuum flasks thermoses even after cleaning it, you can try soaking it in a mixture of vinegar and water or baking soda and water for a few hours to help neutralize any lingering odors or flavors.

By cleaning your stainless steel water bottle with straw regularly and thoroughly, you can help prevent a metallic taste and keep your bottle in good condition for long-term use.