Chlorine Bleach (diluted) This will rehalogenate the silver into silver chloride
You'll also form silver oxide. Which is probably not a big issue since it'll likely float away. It doesn't dissolve and won't plate out back on the walls of the container.
Can I still use it to store and reuse fixer?
Yes, you can still use the container to store fixer even with the silver plated onto the walls. However, I'd recommend filtering the fixer before use, since the silver has a habit of crumbling off of the walls of the bottle, leaving tiny flakes that embed themselves into the emulsion of the film you process. So cleaning the bottle is a good idea.
It's also a good idea to not overuse your fixer. Personally I don't re-use fixer and instead use a more dilute fixer one-shot, so it's discarded after a single use. No more problems with plated-out silver. Fixer is relatively cheap, so I find it a worthwhile compromise.