I’ve tried testicle pumping a little.
The testicles are dynamic tissue, like the penis they can become temporarily larger or smaller depending on blood flow. Unlike the penis, they’re immunologically unique and it’s not a good idea to introduce any trauma to the area that could invite the immune system to sterilize your spermatogenic cells.
I have had mixed results from testicle pumping. Pumping inevitably produces scrotum swelling. I’ve experienced temporary testicle enlargement a few times, but more often shrinking and loss of firmness in the testis.
Interestingly, you don’t have to pump the testicles directly swell the scrotum as penis pumping can do the same thing. The space under the skin of the penis is connected to the space between the testicles and the scrotum. Any fluid build up in that space, not talking about skin edema here, will naturally collect in the scrotum area.
This is why some people who inject sterile saline (one hopes it’s actually sterile and normotonic) or other things into the scrotum actually inject it into the skin just above the penis and why over filling the scrotum can cause the skin of the penis to inflate.
I urge caution with scrotal pumping or injection. It’s a very ugly thing you get an infection there since it the infectious fluid would spread across part of the abdomen, scrotum, and penis. And certainly don’t inject anything directly into the testicle itself, drawing the immune system there, which could be done just by the act of penetrating it with a needle, is how you chemically castrate yourself.
With that said, all you have to do to temporarily enlarge the actual testicles is get blue balls.
Starting: 7"bplx5.2" 2017 (shrunk from disuse)(originally 8"bplx4.5", gained to 9"bplx6")
Current: 9.0"bplx6.125" 2020
Goal: 11.5"bplx7" 2021.