See previous parts here.
I’m not quite sure who “officially” invented this idea of human toilets. Most likely it’s something very obvious, though the real world implementation are different.
While the secret desires of the western society transform into kinky bathrooms (see Fetish toilets, urinals, sinks and taps. Part IV), the Japanese have their own term for both real men and drawn characters: niku benki (肉便器). Literally “toilet meat”. Niku benki is a person sitting in the toilet and providing “a cock service”. You can see “肉便器” written on some poor bound girls and boys on the 22 images below and in the previous parts.