It's just not worth the trouble trying to keep a 2% sodium sulphite solution for use as hypo clear. It must be the cheapest solution used in home processing, so why not just mix up a new batch for each new batch of film or paper and discard after use. If you're doing a lot of processing you can keep it for a few days, but just discard it once it goes off.
You shouldn't then have any concerns about capacity or contamination, or encounter any mould.
HCA is probably also something that does not need to be formulated very precisely; unlike developer or fix, you can probably get away with teaspoon measures once you work out much your current batch of sodium sulphite weighs in your standard teaspoon measure, and how many teaspoons you need for a given volume of water.
done that. it's about 4 tbspoons /liter,but the stuff is expensive and apparently not ver good for fish ,washing off their slimy coat.