Just drop in a tablet, let it sit for 15–30 minutes, and rinse!
Promising review: "I seriously can't believe how well these little tablets work. I had the most disgusting HydroFlask coffee mug — I tried everything. Bottle brush, different kinds of soap, vinegar, EVERYTHING, and there was still a seemingly impenetrable layer of black sludge inside. It grossed me out so much that I bought ANOTHER HydroFlask to replace it. Now eventually they both got black inside, so I tried these little magic tablets. I let a tablet sit in each of my mugs for an hour or two, and the black sludge rinsed out COMPLETELY, without even scrubbing. They look brand new. What a magical product. No weird smell or taste afterward, either. I liked it so much I used it on another HydroFlask I use primarily to hold my Bloody Mary mix in the fridge. I couldn't put anything else in it because it would always taste like spicy tomato juice. Bottle Bright to the rescue! No residual smell or taste anymore. AMAZING, AMAZING, AMAZING." —Amazon Customer
Get a 12-pack from Amazon for $8.
Read more about why people love these no-scrub tablets so much!