Drink it all

A Mistress pissing down the throat of her owned slave.
A slave should drink whenever his Mistress says.

Such an intimate act...to be allowed the honor of directly drinking from her body. Her golden nectar truly becomes part of him.

And personally, I consider it a "mark of ownership" reserved for an owned slave. For he is bound to her. She marks her property by pissing on him and in him. He will learn to crave drinking from his Mistress and he will learn to be the perfect urinal for Her to use. And he will love it.