Printables link. Apologies for the... very lazy select + background blur. In the land of windows I would have used paint.net, but I'm coming to you from a mac today and haven't found a great alternative.
Sorry to burst your bubble but these have been a thing since at least the 90s
Oh, I know. I was a child in this era and wanted something similar for my kids.
I just wanted something that could attach to a more sturdy bottle as 2L soda bottles are... pretty flimsy when a kid is shaking them around to get a vortex to start.