i see what you are saing about the semen backing up into the bladder, but what chia says is that its possible to attain cllmax with NO ejaculation at all, that means the semen does not leave it home, there is no movement of semen at all, so it doesn't back up into anywhere.
not saying i believe that, but he says its possible, and he has lots of lots of testimonials of people who say they have succeeded at his method.