I use a simple gravity fed one
I duc taped a small pastic container to the wall above my cube and have a tube coming out of the bottom that goes into the cube and hangs at my preffered water level. When the level goes down air goes up the tube into the container and water goes into the cube again until the end of the tubing is once again submerged.
right now I am working on a design for a plexiglass HOB design a that would attach to the back.