As a good urologist told me many years ago - the healthiest thing you can do for a prostate gland is to empty it - often. You do that through ejaculation. Yes, if you ejaculate once and then again within the next half hour to an hour there will be more seminal fluid in your ejaculate. Arousal creates more seminal fluid - not sperm, the fluid. (Sperm accounts for less than 1% of the fluid in the prostate.) A woman's arousal creates lubricant, a man's creates seminal fluid. The prostate is only one piece and it may look like two because the pictures show it wrapped around the urethra which goes straight through it.
Your prostate wraps entirely around your urethra and as long as you can pee without hindrance there is nothing blocking your flow of semen. A massage from the anterior is simply a different method of arousal and provides no greater release of semen than a good old fashioned orgasm.
Well it's not really about unclogging. Depending on how old you are you might have enlargement or infection. You need antibiotics for infections and need to see a doctor. Even natural supplements are very helpful to improve prostate health. Read up on super beta prostate supplement reviews in your spare time and you can learn more about why beta-sitosterol works so well.