I think the kiln's were 30' in diameter. They're about 30 or so miles from here but I havent been there yet. (Wildwood canyon, death valley ca) Washing the raw clay just to get any unwanted impurities out. The last 3 shots were from 08' when I was in Southern Missouri down in the Ozarks, #2 & 3 are my sandstone mining efforts, the clay I found was mostly in between the larger hunks like the one in #3 with some on the surface. Shot #4 was how I was processing the raw clay back then, but I've since realized I would have been better having dug a pit out and lined it with sand(stone) to let more of the moisture leech out as the kiddie pool took a few months to dry out enough to work with. The plan for the clay was mostly for making ceramic's goods that I could sell (Hence the need to remove impurities), the sandstone was in the way of where I wanted to garden mostly, figured I'd think of something to do with it later like a tool shed, small charcoal kiln for my blacksmithing & foundry needs or at least a BBQ grill big enough for a small village. But, family sucks and life goes on no?
We are right on the edge of what is called the 'Claybelt' here... I can walk out to any one of a dozen or more spots (in the warmer weather), and dig all the pure clay I want... literally. Any container works for what you are calling washing it.... I just consider it all part of the slaking process... toss the raw clay into a container (a cement mixer is really awesome for this although it limits you to that size of a batch.... big plastic barrels and a stick work just as well...) add some water and let sit for a while, stir (or turn the mixer on) for a couple of minutes, repeat every every little while until it has formed the slip. Then pour the slip through a heavy screen and you're done....