Ive heard of this. People do indeed do fluid injections of breasts, penises, labia and balls. I've even seen a video of a guy who did his forehead.

Most of my knowledge if from men who inject there balls. It seems that some can take great amounts of injection and not worry about fluid overload. It takes hours to reabsorb at a slow rate. Were talking 4-8 hours. All the same I probably would not go over 2 cups total since ive never seen anyone else go over that. The point of the saline injection is to get it under the skin. Especially in the breast area you do not want to pump the saline into the ducts. It only goes under the skin.

I dont have any idea what it feels like but the people describe it as being similar to using a pump like for example on the labia. The tightness and sensitivity. The heaviness and squishiness.

As for equipment there are body mod shops that sell I.V. kits for this purpose.

Also to echo what was said above. Be sure the needles are new and clean, the area sterilized, gloves being worn, and saline from a good source.