https://menrus.co.uk/sex-content/saline-injections/
Saline injections (balls)
Saline injections are injections of sterile 0.9% salt water solution into the ball sack (scrotum) to make it temporarily larger. For those who engage in recreational saline play, the practice is also referred to as saline or scrotal injections, scrotal infusion, or scrotal inflation.
Despite the common name of the procedure, it’s important to note that saline is injected into the ball sack NOT the balls (testicles). The ball sack is elastic and can stretch to a greater size. The sack can be inflated to the size of a large grapefruit, the appearance likened to that of a water balloon. Though the cock can be enlarged this way, the ball sack is easier and ‘safer’ to inflate. This can go hand in hand with a ball sack stretching fetish.