Based on known anatomy- I’d have to say that it would be more likely to be in the position of a horse- as centaur are classically human above the mason Dixon- and horse below- so genitals being below the “human” part would imply horse...
However- we don’t really know. Centaur could have some sort of retractable genitals that come from within the body. Depending on the cannon- centaur may it may not be able to mate with humans- so case by case this would give us SOME idea about their genitals and anatomy. However where they cannot, or we do not know- there is no reason to think they have a penis as we know it. They could have some sort of Cloaca like a bird, or spray a mist... or females could have the protruding or “penetrating” genitals.
Theories of known evolution would suggest that centaur May mate face to face- it’s believed that much of the development of humans into what we are was due to face to face love making. So the human elements of centaurs and their societies suggest perhaps they do make love face to face? Of course- again- mythologies differ and in many- centaurs didn’t evolve but are magical in nature- meaning rules and logic of evolution and known biology may not apply.
For peeing
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Yeah peeing
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