One of the common side effects of the drug Tamsulosin, the main ingredient in Conti Flo, Flomax etc, is retrograde ejaculation. This occurs when the bladder sphincter muscle does not contract before ejaculation thus leading to a discharge of seminal fluid into the bladder instead of its wending a merry way down the urethra.
Try not to think about that when engaged in bedroom activities. It's somewhat disruptive to man vibes. It might help to regard the process as a primitive form of birth control known in the appropriate parlance as coitus saxonicus. This was possibly invented by the inhabitants of Wessex shortly before the Norman conquest and the introduction of french letters into the UK.