by AlanMcD » Thu Feb 19, 2015 9:31 am
Always feed the valve in from the fill port end. The only hole to worry about that way is the gauge port. As the oring becomes visible in the hole, it begins to extrude out into the hole from the constraining pressure the rest of the way around the tube - you need to push it back in there as you move it into position. I just use my thumb to get most of it in there, but I typically use a wide flat blade of a screw driver to push it down the last little bit as I push it the rest of thway into position. Use plenty of silicone greese as you do it. If you think the o-ring got nicked as you do this, pull it out ans start over.
The first time I did this, I bought the exact number of o-rings to do the job (4). During that process I learned that 0-rings are expendable, and ended up buying a bulk pack of them for not much more money. If you are a tinkerer, you will be pulling things apart several times per year. Your only constraint is that you hand pump - and once you have a tank and compressor, you won't think twice about it as you have all the compressed air you need . . . .
Leaks happen. Just fix them when they do occur.