I am 20 years old and have found a small sack inside my scrotum about 3 years ago that isn't attached to either of my testicles. If it's squeezed, it feels like some liquid will move through something like a vein and back into some organ maybe intestines(not really sure) or something in the area around my belly-button (lower-chest). Once squeezed the sack will disappear when I'm laying down and then when I stand back up it comes back within 20 mins or so. I havent been to the doctor yet, but I need some ideas of what It might be so I can better explain it to the doctor. I looked it up about a year about and I found out exactly what It was but now I can't remember what it was called. Could you provide me with some possible problems, thanks!

PS. THE SACK IS PAINLESS!!!