Ah, my boys peed in the sink for a few months while growing up. It actually helped their aim. They grew out of it after a while.
You just run some water down after it or, y'know, clean your sink every day or two lile a normal human.
You can also just two fingers spread and pull up on your pubic area a bit. I don't quite know how to describe it, but directions are out there.
I told a friend of mine this and showed her (this was late dial-up internet era), and she said ''That's dumb, that wouldn't work.''
A couple days later she shows up, goes to the bathroom, and yells to me "Come here.... LOOK WHAT I CAN DO!"
Yes, my friends are weird like that, especially back in the day.