Regarding the blank...
Our place in Tucson is on a couple of acres and I just walked (carefully - there be lots of sharp things and snakes in these parts) around looking for dead cholla. There's a lot of cholla around. Some had been dead long enough they had collapsed to the ground - others were still upright, but denuded of any skin/thorns. I was looking for stuff that was relatively straight, in the "sweet" spot of thickness (3/4") and with a center hole that wasn't too off center. By center hole, I mean the hollow bit down the middle. On some cholla arms, that hollow bit can be way off center, which doesn't leave you enough thickness on one side of the blank.
Some I cleaned by blowing air, some I cleaned by washing out (and then oven drying). To fill them, I wrapped them up in green tape, leaving an inch or so extra at the top to form a reservoir. Poured the Allumilite in slowly, and had to wait and repour a time or two as it takes a little time for it to settle down into the blank. I filled it over the top and into the reservoir so there would be some extra to fill in the air bubbles that the pressure would force out. I think I got this technique from a post by Exotic Ed. All this went into the pressure pot at about 30psi, and I just let it sit there all night.
Nothing to special about turning them other than to make sure you center on the hollow part of the cholla. More often than not I have to do a little CA fill here or there, but nothing thats too much of a bother.