This model demonstrates the siphoning action that makes the modern flush toilet possible. If you fill the bowl slowly, the water trickles over the apex of the siphon tube behind the bowl. That's how the bowl finds its natural fill level. If you add more water suddenly, the siphon tube fills and suction pulls most of the water out of the bowl.

I've marked this a work in progress because I made a few additional tweaks to the model after my last print. Both of my test prints worked, but the uploaded model has a nicer surface mesh and fixes a spot where I made the back too thin in the second test print. I'm now too low on natural ABS to print it in the proper color.

(I really wanted to make this in OpenSCAD just for the mashup possibilities, but first it annoyed me by not having recursion and then it infuriated me when I bumped F3 and it lost all my work...)

Choose your skeining parameters carefully. In order to flush the model must be water (and air!) tight. If there are any leaks in the siphon tube it won't work. To help skeinforge along I have inserted a tiny open disc just above a trouble spot in the plumbing. This should cause it to double up on solid layers at the apex of the tube. You can see this disc in the section view between the fill hole and the siphon tube.

The bowl is 2mm thick and your thread width will determine how it prints. Anything under 0.5mm should get 4 thicknesses and anything greater will print as two nested shells (which worked for me).

There are M3 mounting holes for a tank if you want to get fancy!