I have put a special mouth gag on my slave that will make him drink all of my piss. From the outside, the gag looks like a urinal and ends with a pipe directly in my slave´s mouth. If I now pee into his gag, the piss will automatically flow into his mouth... I've also put him in handcuffs and told him that I'll only unlock them as soon as he's swallowed all of my golden shower.