The easy way to clean a drinking tube.
Start with a filthy platypus tube like this one, and thread some wire through it
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Use the wire to thread some cotton through the tube.
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Use the cotton to thread some rough string (e.g. bootlace)
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Fill the whole lot with water
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Shove it in the freezer for half an hour
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Pull out the iced string...
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... and viola - a beautiful clean tube!
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