Thats what alot of people think but thats not true. You kidneys have to process it forst. When you overload your kidneys you get....... kidney failure and dialysis. If that was true then we would urinate out everything our body didnt need (exta food, fat, oil, etc)
Edited to add thats how people get drunk, too much alcohol for the body to process and it floods the system. Urinating will not relieve a hangover, you have to wait until your kidneys flush it out of your blood stream.