I had a soap dish that was similar to this at home that was made from wood. I thought that it would make for a fun and useful 3D print once finished.
This soap dish features a rounded depression in the center where the soap sits. Openings along the depression allow water to easily flow through and empty into the sink.
Just print up this soap dish and finish it smooth it out with something like Smooth-On XTC.
This soap dish measures approximately 4 inches by 3 inches by 1 inch. It can be scaled up or down pretty reliably.