The problem is you obviously know your key is frozen in ice and therefore could spit out a cube when you tasted piss, knowing it wasn't the cube that would finally give you the opportunity to unlock yourself and jerk that mess from your balls. Well I'm an intelligent woman and therefore this is a two part task.
Part B
1) If you spit out a piss cube while playing the game, the task counts as a failure and you no longer have cube you get for maintaining this task throughout your period of chastity.
So the choice is yours, do you want to swallow your own piss to increase the chance of an early orgasm.