Mythbusters actually proved it can happen. At the end of the episode they actually do pee on a rail and get a buzz, should he have not been so nervous and had a steadier stream, he would have gotten a real surprize. You Fail at watching TV.
Its not the porcelain thats conducting its going through the metal to the water which can conduct. and further more the porcelain if anything acts as a nonconductor to hold the current in the water.
