Ok, I put some diagrams together. I'm not too sure about the shading inside the cylinder, I think it might confuse things, so I'd be happy to hear other peoples comments.
Tony, it's quite easy to move connections, heaters etc, so let me know what permutations and arrangements you want for the page. We can use or loose the ticks and crosses as you see fit. Do you want all the designs on one graphic or individually? Would it be an idea to name the various connections as in a heating sytem?
I could show foam insulation, along with additional insulation on the bottom of the tank when up-turned, if you want to include that in the text too.
I haven't had a chance to ask my mate how common primatic cylinders are.
Efforts to date (just a scratch file ) are ...
I've also up loaded photos of soldering new connections to a cylinder here ...