The Tantalus cup works normally if it is partially filled. If filled to the brim most of the liquid siphons out through the bottom. It is also called a Pythagorean cup.

Thing:17330 by Scooter46290 is a such a cup with a simple but elegant siphon composed of three concentric cones about a central tube. Here is another version where the siphon is concealed in the stem. It has the advantage that the siphon has a greater head and can more completely empty the cup. Open scad and stl files are provided.

There was a leakage problem in early versions. The siphon always worked well. The problem occured when the cup was partially filled. Liquid leaked through the wall of the central stem and slowly trickled out the bottom.

Printing with 100% infill, one shell, and 0.2 mm layer height solved the problem. Playing the gcode files in netfabb Studio was helpful in deciding which parameters to use.

On my Replicator the cup takes a bit under 3 hours to print using 100% infill, one shell, and 0.2 mm layer height. It was printed directly on the build platform.