Mash Tun Help

So I'm in the process of converting this:



Into a MLT. It's a 10gallon double walled stainless steel vessel that was once used to transport large quantities of soup.

Anyway, a couple of questions:

1) I assumed there was foam in between the walls. When I drilled the hole for the valve though, I found it was just air... or lack thereof actually. When I first breached the wall, there was a sucking sound. Obviously a vacuum in between the walls. How poorly is this going to insulate the wort now that the vacuum between the walls is gone? Should I even bother continuing with the project?

2) Because the inside of the vessel has a rounded transition from the wall to the base, the closest I could get the brass fitting that will connect to the manifold is a half-inch or so up off the bottom. I'm assuming there's not much I can do about this? I'll bend the tubing so the majority of the manifold sits on the bottom, but once you get below that exit point, will the siphon be enough to pull that last half-inch of wort out? Any suggestions in this regard?

3) I used some silicone caulking between the inside brass fitting and stainless steel washer and the vessel wall. I had a rubber o-ring as well, but even the biggest one I could find locally was just a tiny bit to small for my liking. I wanted to ensure no leakage. On second thought however, I worry that the silicone might not be good in terms of wort contact. The instructions I found called for a silicone o-ring (which I couldn't find) so I figured the caulking (once dried) would be the same... but maybe not. Thoughts??

Thanks!

Are you using this like a cooler MLT or are you placing it on a burner? If you're not using it on a burner I would by a piece of polypro sheeting
http://freckleface.com/shopsite_sc/store/html/polypropylenesheet.html
and cut it out to fit in the bottom, then sit your manifold on top of it. This will reduce your dead space.
If you are using it on a burner I think it might get too hot and warp.

Insulation is often trapped air, so air should not be a problem. My mash tun is the same, with a half inch at the bottom why worry about a cup of wort, you can make more. I have used silicone caulking too, so it will be ok or we will each have the same problem.

awesome. thanks gents!!

not a direct burn. i'll check out the poly-pro... once i determine exactly how much water it is. if it's just a cup or so of wort... i think i'm with brieux - just make more! LOL

Where did you put the bulkhead hole? I would have done it in the bottom, dead center and then put a perforated stainless false bottom over it.