There are a lot of them. If I remember any I will update you XD
BJ Alex ( in one of the chapters there is a scene where the uke pees) (╯°Д °)╯
Sokuochi Yarichin Yankee ( the second chapter of the first couple there is scene where the uke pees) Σ(っ°Д °;)っ
So far those are the only ones I know of that do that but if I find some more I will let you know. (●'◡'●)ﾉ
Oof I forgot about this. I actually remember some yaoi which have this type of stuff
http://www.mangago.me/read-manga/hashi_no_xl_saizu/ (Chapter 5)
http://www.mangago.me/read-manga/uso_mitai_na_hanashi_desu_ga_h/
http://www.mangago.me/read-manga/hard_core_heart/
Kareshi Glamorous (chapter 1 probably)
Sensei, Anata ni Chikadukitai (probably chapter 1)
http://www.mangago.me/read-manga/iiwakenante_zenbu_uso/
http://www.mangago.me/read-manga/michi_to_no_souguu/ (chapter 2)
This are all I could think of. I will still update you if I find more
Why is any uke peeing while they are fucking so hot to me? Thinking about it makes it seem like it would be a mess and would be stinky but still HOT. I need Jesus. No. WE need Jesus