I don't see any real reason to soak a stem in alcohol. There are some stems that don't take to kindly to alcohol soaks,especially nylon( some Medico) early ABS (used in some Grabows from the 80's) and some other types of plastics. Vulcanite and Acrylics are not usually hurt by soaking them,but I see no reason for a long soak. If you clean them well inside with alcohol,and wipe them down well outside with a cloth soaked in alcohol it would, I would think, be sterile. Just my two cents worth.