To create a waterfall effect down the glass surface, I need to bring water up along the back side of the glass, come over the top edge of the glass, and then travel along the top edge of the glass. Trying to cobble something together from the myriad of pipe fittings sold in hardware stores ended up being a fiasco that would take up a lot of space, so I decided to model and 3D print what I really wanted.

This part is designed to accept 5/8" outer diameter clear vinyl tubing in each port via compression fitting. The part is made to sit snugly on the top edge of the glass. Water comes up in the back and is redirected over the glass edge and out a side port on the other side. 

To mitigate potential leaking, I sealed the exterior of the part with a plastic epoxy. The .stl files can be found at http://www.thingiverse.com/thing:329725  and brief video highlights of the print (which can help visualize the internal construction) are uploaded at http://youtu.be/7OoFe0CkZio. Here is a picture of the end result: