That looks awesome! I'm also curious about the stone box.
Me too. Did you contruct it? What kind of rock? How is it sealed?
It is made with old slate pavers that had been sitting in a pile in my parents back yard for about 20 years. Figured out my dimensions and cut them to size with a tile saw. I used a food grade silicone to seal them together and built wooden collars to wrap around the top and bottom to keep the walls from pushing out when it is filled so I am not relying entirely on silicone. I built a wooden lid for it as well.
It weighs about 50 pounds empty so I have it on a piece of thick plywood that is a little bit larger than the footprint of the fermenter. I created rope handles on two sides so I can pick it up and move it. When I am racking out of it I will pick up one corner of the plywood and set it on a 2x4 and set the racking cane in the low corner I create by doing this. I can rack out almost everything and have very little waste.
It is easy to scoop yeast out of the bottom but it is a bit of a pain to clean. I scoop out as much as I can and then fill with warm/hot water and get everything as mixed up as I can and then sifon out. I usually have to do this a few times and typically will put in some oxyclean to help me break up any crud. Once it is clean I usually fill it with starsan. I don't leave the starsan in for extended periods because I think the acidity interacts with the slate.
So far it has been really fun to use and made some pretty good beer.
Check out my blog to see some more pictures: http://saccharomycessafari.blogspot.com