This is a u-bend pipe for attaching a 1L pop bottle to a hollow stainless-steel curtain rod. It will function as a child-powered marble lift, for a marble run I'm building for my kid.This is UNTESTED - I don't have a 3D printer. But I don't think I can make any more improvements without printing it, so I'm going to call it done for now. I'd be especially interested to know if the overhangs are a problem for the makerbot or any of the other FDM machines.Edit: cleaned out a random triangle in the thread region. Edit: aaaaaand I guess I ought to regenerate the stl after i do that... Edit: Added a top piece; moved everything to positive z coordinates.Cut the bottom off of a 1L pop bottle. Find a closed cylindrical cardboard tube which fits over the bottomless bottle snugly (I have one of those display tubes for single-malt whisky bottles, which fits nicely over a Loka carbonated water bottle). These two things make a cheap air pump. Next get a curtain rod. I have a 4 foot one; it's stainless steel and white. The inside diameter should be abou 16mm, because then ordinary marbles will roll freely down it, without any extra space.Use a hose clamp to attach the curtain rod to the base. Hopefully the fingers around the top will compress a bit without breaking.You now basically have a child-powered marble cannon, aimed at the ceiling... so put the top piece on the other end of the pipe, with the same hose clamping method. This will at least aim the marbles downward again. I intend to use some spiral cable wrap at this point to redirect the marble where it needs to go. To use this, drop marbles into the bottle, place the cardboard tube over top, and launch.Printing out the part is nontrivial for me, since I don't actually have a printer! I haven't made one of these yet, so no guarantees that it works as described. The bottom piece is a pretty big hunk of plastic, so the normal fab shops are kind of expensive. So, uh, if anyone is making one of these, please consider making 2, and I'll buy one! I'll post pictures when I have a working part.