Again I appreciate the comments guys!
BigBulli...I know what you mean....my casting has many improvements needed still. One problem is my resin has now reached its two year shelf life so its getting harder to keep air bubbles out. The main thing is keeping the moisture out. There are ways around that but I'm cheap!

Vacuuming is the best way..I built a vacuum chamber out of an cast aluminum cooking pot and an old refrigerator pump.
A few things I forgot to note though if your actually going to make one.....
When molding the silicone divider/support plug you can mold it in the same size glass tube you are using. You want that plug to slide easily up in the tube. For a while I was using it with no divider but I found it turns all the juice dark and starts to taste nasty by the end of the tankful..I guess because it mixes with the condensation. This way the tank stays clean the same as when you fill it.
You can also find a tube of plastic or whatever and mold a whole rod of silicone..then just cut off the length you need with a razor. Dont use glass tube to do that though.....as it will bond to glass if its clean and dry and you will either break the tube or dig it out in little pieces...dont ask!

Use a mold release or some cooking oil too.
Be sure to make your mod have at least a small air space all around the tube so the heat wont warp your mod...and so the tube is free to expand and contract without cracking. I made the space for the atty the same size as I made for the battery....about .1" larger in diameter than an 18650...that gives it a .050" air gap all around it to dissipate the heat. The connector keeps the atty centered in the space and the MP tube does at the top. It gets hot around the atty but stays localized within about an inch or so...also be sure the batt compartment is divided so the heat wont get to it. The first one I did I didnt do that so I added a flap of insulator material between them.
If you decide to get Pyrex tube I would get Medium wall stuff...I'm using the standard wall and you have to be more careful cleaning and removing the plugs.
This is a good site for working with the glass tube...at the very minimum you should know how to cut, flame polish and stress relieve it...none of it rocket science...and fun.
The Scientific Glassblowing Learning Center: Home Page