It all depends on the partner, sexual act and the reason behind it.
If it's more of a humiliation thing - human toilet or simply pissing on them to show dominance.
If it's more of a playful thing - watching you SO pissing outdoors for the fun of it or wetting himself/herself.
If it's more of a sex thing - where you enjoy it because it's piss.
In my case, I've only done the playful thing. Humiliation depends if my fuck toy wants that or not, I don't mind pissing on him/her if it gets them off. As for using pee in regular sex, I'm not interested.
So to be more accurate, I'm into it, but only in certain aspects. Only thing that would turn me on would be act of human toilet pretty much, because that means they've surrendered completely to your will, no matter what. In the end it's more about total control than piss itself.