For me I kinda eased it into a conversation. We were talking about fetishes with each other and what types we had. I slipped in that I "once" had a piss fetish and she was quickly intrigued by that. I told her my experiences in it and she wanted to try for herself.
At first she only really pissed in the bath tub, easy clean up, not the toilet, it was a good start for her.
Then I was slowly able to ease her into going other places
Eventually she worked up the courage to spice it up a little. One night we were hanging out and she drank a lot of water that day. She eventually had