Chinese Herbalist in 珊瑚寶 Sauna

Yeah, it sounds logical.  A friend of mine said your balls are in a closed environment, muscles contract and eject.  Load comes out - something must go in, that is ‘採陰補陽,' he said. The question I have is, does it really simulate a vacuum tube, or it will burst?   He even says without that suck back, you wouldn't get most of the VD!   I am not a doctor nor a biologist, maybe some ching here call tell the truth.