Powder in double plastic bags...In a plastic tool box.
Mixed solution in a glass jug in the closet....
I do not reuse much if any sulfite solution...I do catch Jim pouring some back into the jug occasionally after rinsing a carboy.
I prefer to pitch it after a session of rinsing tubing, racking canes, spigots, buckets, etc. I pour a good amount into a stainless bowl and rinse and splash out of that, or out of a bucket.
It's cheap and I figure that most of the equipment has been first rinsed with water, so figure the solution is getting diluted by the end of a session....so out it goes.