Semen is human life essence. It is only necessary to discharge it in the act of procreation, in which you contribute a part of your own life force to jumpstart the life of another being. Why do you voluntarily expunge it from your body as if it were mere sludge in a drain pipe? Have your sinful ways taught you nothing? Are you not tired after foolishly expelling your own quintessence day after day for purely hedonistic reasons?
For your own well-being and salvation, I urge you to keep idle hands away from the genitals.