A few more pictures, by popular demand...
My mom asked where the vault is in relation to the trailer, so I offer you this shot to help illustrate. This picture is shot from the top of the trench looking down, before we finished the trench or put the pipe in it. The vault is just to the left of the trailer (it's not installed in this picture, but you wouldn't be able to see it here anyway). it's actually about ten feet from the trailer, so very close.
If you look at a closeup of this picture, you can see my solar compass. This is something that Quentin Branch showed us how to do at a rammed earth workshop he taught last year.
I'm afraid the composition on this shot is quite poor - it looks like it's a picture of a weathered agave flower stalk lying on the lovely red dirt. In fact, the important things to look at are the foundation stake and the little bamboo stakes. This is why you need the close-up. What you do is that you put the stake in and get it as close to vertical as you can with a level. Then at about 11:00 you start putting bamboo stakes in the ground at the top end of the stake's shadow. Every ten minutes, you put in another stake.
At some point, it becomes clear which stake is closest to the big stake. This stake is the one that's closest to solar noon. The line between this stake and the big stake runs across the axis of solar north and solar south. Why is this important? If you face your house due south, then the windows on the south side will be shaded all day in the summer, and sunny all day in the winter. You can use a compass to guesstimate this, but magnetic north is a bit off of solar north, so it's good to do it the hard way. The cool thing is that I've done the solar compass several times, and I've gotten quite consistent results, so I think I'm doing it right.