I bought some parts for getting started. The parts on the left should later become the clay extruder and the parts on the right should later become the sand extruder.

A few parts are still missing like 3D printed parts to hold everything together.

I found a way to use the sand/powder extruder in a vertical orientation to save a lot of space. The sand exits the extruder through the side port of the T fitting only when the drill inside is moving. I will also add a 3D printed nozzle to the sand outlet to bring the sand as close to the clay nozzle as possible.