I meant that whether someone injects something into their scrotum has nothing to do with what or how much they ejaculate. The scrotum is basically a sinus cavity. It's not even connected to the testicles and various related tubes in there. So you could put a gallon of saline into your balls, but you won't be able to ejaculate it out.
The only possible effect that could have would be that as your body absorbs the saline that the hydration rate for the whole area of the body increases which 'could' have a slight effect on volume of cum, but it's more likely the person would just piss more.
The key word in my original post was "vasectomy".
Indeed, in one such video there is even evidence of the vasectomy scar on his scrotum(assuming they are all of the same person, whose off-site username I won't repeat but can be found by searching for "saline injection" on LPSG in one or two of the dozens of threads that appear every few months), though I can't find the precise thread in which the scar itself is discussed.
Hence, the necessary opening for this to work - from the vans deferens to the scrotum interior - is made. How or why the openings aren't completely clipped shut, however, I cannot say.
Everything you've said about the scrotum is correct in a normal situation but the subject in question, and the surgery he's undergone, changes what assumptions can be made. It's been discussed many times and by far more knowledgeable people than myself, much of which you can read by using the aforementioned search terms. :smile: