I don't understand how you don't grasp the concept of all this. Especially if you say you are bisexual, it's even more puzzling how other people's personal preferences would confuse you.
Sexuality and attraction, like many other things, are different from person to person. How could you judge someone else for being attracted to something that you are not when you yourself are attracted to things that not everyone else is? This makes you a hypocrite and shows how much more growing and learning you need to do as a person.
The request was for a piss video, a common sexual fetish. If it's not your cup of tea (or pee) then just move on, but calling it nasty and dirty while associating it with scat is just plain ignorant. That is the same hateful, despicable strategy that extremist use against the LGBT+ community when they have no basis for an argument except pure hate and lack of an IQ. "oh they are gay, they must be a pedophile too" sounds a lot like "oh they like piss, they must like scat too".
Stop judging people to mask your own shortcomings.