Perhaps you’ve seen this idea floating around. I decided to try it myself today to see how it works. You can see from the photos that it works great! I used a sharp knife to start the cut on my bottle (2-liter) and then used scissors to finish and smooth the cut.
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NOTES: The nice thing about doing this, as opposed to just using a rubber band or something, is that you can actually pour the chips/rice/etc. from the spout. I think for the butterscotch chips (as pictured) I will use a milk carton lid, though because it’s a little wider.
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Overall, a great idea. I will be reusing my bottle tops from now on!

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