Congrats on getting the T20! Not sure on the T20 but my Olight M20 has 5 "O" rings installed in it. It has 2 on the battery tube at the tailcap end, 2 on the battery tube at the head end, and one on the head between the head and the clear glass lens. Mine also came with a glow in the dark switch boot but I haven't installed it yet either. I haven't found the right tool to remove the retaining ring inside the tail cap. Inside the tail cap there are two small indentions directly across from each other (at least on the M20). I believe you have to find something to fit into those indentions and unscrew the retaining ring. I've read some have used a small needle nose pliers, a small scissors, etc. I don't know about the T20 but I've read the M20 can tail stand if the glow in the dark switch boot is installed. I've also read that it still can't so I want to get it switched so I can find out for sure. To bad they don't include some kind of removable plastic collar that would fit over the tail end that would allow the light to tail stand regardless of the type of switch/boot configuration.