The fluid stored in a little reservoir in the abdomen. We are only talking about 100 or so millilitres of saline and it’s a closed system.

When you want an erection you pump the fluid into the penile implants and when you’re done you open the valve and it drains back into the reservoir.

Apart from penile implants the same system albeit with different fittings are used for urinary and faecal incontinence replacing the sphincters that control urine flow or bowel movements.

In men the pump is placed in the scrotum and in women it’s placed in the labia.

The penile implants apparently are prone to slippage and even eroding their way out of the penis. I bet those happen way more often in the skin tubes these women get.