was a piece of plastic you could buy at toy stores or dollar stores,
probably science stores too, that connected two two liter bottles of
soda at their openings. If it had a longer history and was sold at
hardware stores, it would be called something like “a two-sided female”
for each of the male ends of the two liter soda bottles. The idea was
that you could fill one of the bottles with water, then connect another
with this piece of plastic so the second vertically mirrored the first.
Once the connection was snug and airtight, you could flip the bottles
and the water would fall from the top to the bottom in a visually
satisfying cyclonic spin. Like watching the circling of the drain from
the inside. Like watching your insides drop into the ground.