There are reusable silicon mother's breast milk/formula baby bottles, as well as disposable sacks for baby bottles, which use a soft silicon nipple, in various flows, including slow for smaller babies, in four oz and large sizes, that might work for both storage and dispensing chemistry, by sealing the factory release hole and then using needles to withdraw material, as needed and in self-sealing fashion, without air filling the bladder.
Amazon carries these, under the Playtex brand.