I have replaced the tail of mine before so I can finally answer something. (yay!)

To remove it:

1) remove the rubber band that stretches down under the tail.
2) Detach the control lines from the flappy thingies.
3) Turn the plane upside down and remove the 2 screws on the bottom. (you need a small screwdriver!)
4) after you unscrew it, the tail just simply falls off.

I'll try and measure the tube for ya.

WARNING: Do not climb the tree! I got a serious case of poison ivy and had a needle go into my arm at the doctors today.