Handle it, store it, get rid of it
Home developing uses small amounts of fairly ordinary chemistry, but it still deserves respect. This is what I do. The authorities are the label, the safety data sheet and your local waste rules.
Read the label and the maker's Safety Data Sheet (SDS) for every product before you mix it. Ilford, Kodak and the other makers publish an SDS for each product, and your supplier can send you one. If anything here disagrees with the SDS, the SDS is right.
Handling
Ilford's developer sheets recommend that "gloves, eye protection and an apron or overall are worn when handling and mixing all chemicals", and say to follow the health and safety advice on each package. I do exactly that, and I mix powders slowly with a window open so I'm not breathing dust.
- Use measuring jugs and bottles that are only ever used for darkroom work.
- Never store chemistry in drink bottles or anything that looks like food.
- Label every bottle with what's in it, the dilution and the date you mixed it.
- Keep everything out of reach of children and pets.
Getting rid of it
Used fixer contains dissolved silver from the film. Don't pour any photo chemistry into a storm drain, and check your local rules before anything goes down a sink.
In Los Angeles County, the Household Hazardous and Electronic Waste (HHW/E-Waste) Collection Program takes household hazardous waste for free. The CleanLA site lists collection events and permanent centres, and the program's phone line is 1-888-CLEAN-LA. Outside the county, your city or county waste department will have its own program.
I keep used fixer in a labelled bottle and take it in with everything else when the bottle is full.
Shelf life
Each product's technical sheet gives storage life and capacity, and they vary a lot between products, so I go by the sheet rather than a rule of thumb. Concentrates in full, tightly closed bottles keep far better than half-empty ones.