The ATF wants to be sure that one is not purchasing ethanol for lab use and diverting it to beverage use without paying the tax. It is possible to purchase pure ethyl alcohol, but there are severe record keeping and tax restrictions. Denatured alcohol is ethanol with something added to make it undrinkable. SD3A is authorized for manufacturing use at facilities that are licensed for its use. It may not be sold to the general public.
Reagent alcohol is a suitable replacement for pure ethanol in almost all laboratory procedures.
Choose a germicide with the level of disinfection appropriate to the device being disinfected. See the labeling for the device or contact the manufacturer for instructions. Sterilants kill all microorganisms when used according to directions. Low level disinfectants are not effective against spore formers or tuberculosis. They may not be effective against all viruses.