The first pee related content I remember was from a soft porn magazine from the 80s called Fantasia. Every now and then they would publish a pee related story. When I was 16 I came across a discarded Fantasia magazine in our works store room. They published a whole double sided page dedicated to peeing and wetting.
Those stories certainly stayed with me until the internet came along, which I think I connected to in 1996. The first pee related porn I watched was from a Japanese site called Giga Maniac. What I remember was that the site had lots of content but was horrible to download because