Well I've taken the plunge and worked on scrotum pumping this past week. And I'm amazed at what I've learned about it.
First off, you've seen those uniball pictures where someone pumps so large it look like one grotesque testicle. What you don't realize until you've tried it, is that that look is tempoary.
I was a bit disappointed this afternoon when I pumped myself a little too big, but in six hours time my scrotum started developing shape again, and looked pleasing to my eye.
From what I have read, and yes newart.com is probably the best site on the topic, this is all temporary as you'd expect. However, it does last a couple of days, and if you spent 20-30 mins a night under vacuum your 'temporary' results would be well maintained.
Also there is anecdotal evidence that a prolonged regimen of this will lead to permanent size gains.
Now here's a couple of counter intuitive things I have leaned directly. Low vacuum is best, there is no need to exceed 5 in Hg.
As one friend put it : comfort = time = size.
By placing your scrotum under vacuum, yes you are causing lymph to fill your scrotum, but it also fills the testes enlarging them. So you do get bigger balls, not just a scrotum that feels like an over filled water ballon.
This lymph transfer takes time. Using a high vacuum doesn't really speed the process much, but it will likely cause discomfort, and could lead to blisters and blood spots as mentioned before.
When I started this Monday, I was using 7 inches Hg, and it was difficult to stay under vacuum for more than 10-15 minutes.
When I lowered the vacuum to 5 inches Hg, I was confortable for a full hour. I only pulled out because I was bored of sitting there for a hour. And of course I was very surprised with the result!
Each testicle was 4.5 x 2.5 x 2 inches! And they felt just as natural as ever, just huge!
Anyway, if you have questions I'd love to talk how about my DIY (Do it yourself) engineering came together.
Here are my results: http://www.lpsg.org/members/gbb/albums/ball+pumping/