This is a poorly done instructable but the outcome is great! I will make up for the lack of step by step pictures with a very detailed set of instructions and parts list, I made the whole thing for less than $10.00 US. Money well spent!
The fill valve is installed in the flattest part of the end cap to get a good seal. I used 2 part marine grade epoxy on the inside to seal it as opposed to super glue. It has held for quite some time and seems to be totally air tight. It passed the bubble test, you should put light pressure in the chamber and apply soapy water to all the joints to see if you have any leaks. If there is leaks you will see tiny bubbles.