^ I think part of the "Man of Steel, Woman of Tissue" premise is that involuntary actions like ejaculation can't be held back consciously like everything else Superman does ("World of Cardboard" and all that). I've never actually read the essay.
^ Now, the conversation is getting weird. But I think their bodily functions works the same as human. Think about it, baby Clark wouldn't have been conscious of it, and the Kents would have had a hard time taking care of him if he pissed with the pressure of a fire hose.