Are you trying to remove oxidation from the outside of the stem? Bleach will remove oxidation but it will also pit the stem to point that it has to be sanded and polished again. Bleach can sometimes pit a stem very badly, I wouldn't recommend it. High proof alcohol like everclear or 151works great for simple internal cleaning as does denatured alcohol. IsoPropyl will work in a pinch as well but can have perfumes in it.
If the stems are turning green on the outside the best way to remove that is with abrasives, sandpaper, polishing compounds, fingernail boards, course paper towels, toothpaste, etc. But a stem that has been worked with abrasives will need to be polished.
If your stems are not oxidized I would not soak them in anything. A pipe cleaner dipped in alcohol will clean it out. Try not to get the alcohol on the outside of the stem.