This (quote) is what's holding me back from buying one:
> Not only are these difficult to fill and empty, but cleaning them is a real challenge. Since there's little air circulation within the Klein Bottle, moisture doesn't evaporate. Worse, you can't reach in with a towel. So you'll need to dry the interior surface using alcohol. I've had good luck with a pair of small magnets wrapped in cotton cloth.
My aunt gave me the Klein Stein for graduation (a klein bottle in the shape of a beer mug). It's actually not that hard to clean. You rinse it with water and then bake it in the oven at ~200F for an hour and you're good to go. It is a bit more involved than a normal mug but it's really not as bad as you would expect.
> Not only are these difficult to fill and empty, but cleaning them is a real challenge. Since there's little air circulation within the Klein Bottle, moisture doesn't evaporate. Worse, you can't reach in with a towel. So you'll need to dry the interior surface using alcohol. I've had good luck with a pair of small magnets wrapped in cotton cloth.