pigstick

How do you tell if a tank o-ring is no good anymore?
Also, is there a way to screw the tank in without losing co2 and messing up the o ring? Most of the time I can do it, but every once in a while it just sprays and messes up my ring.
Whenever I do it, I know it's gona happen, but when it does, it startles the bejesus out of me.

No0bIe_PaIntBal

A. if theres any kind of chip or dent in it or if it leaks replace it its like 10 cents so who cares
B. unscrew it till it starts to hiss a lil then unscrew it a like more and itll release the built up co2