Klein Bottles

Remember this from college topology?

Link to a firm that will sell you one.

Interesting instructions are included for filling and drying out the bottles, which include drying in a medium oven, microwaving, rinsing with alcohol (since it evaporates faster), using an aquarium pump and hose, and my personal favorite: expose the water, but not the glass, to a beam of pure antimatter.

Reproduced here is the frightening instructions to clean inside, or is that outside?

I suggest swishing around a small amount of Windex or alcohol. Use Vodka for a Klein Stein. For tough marks on the "inside" (which, of course, is the same as the "outside"), use a pair of small flat rare-earth magnets, each wrapped with soft velcro or cotton, and wet with Windex.

Keeping one magnet on the "outside" (which, of course is the same as the "inside") and one on the "inside" (which, of course is the same as the "outside"), you can scrub both sides of the glass at once. Since both sides are really the same side, so you're really scrubbing two sections of the same side -- a nice labor-saving method that also works on Moebius Loop Conveyor Belts.