Developers are usually one-shot. Dump them down the drain using plenty of water to dilute and wash it away.
However, check the manufacturer's instructions. Some are reusable and/or replenishable. If it is, save it. Otherwise, dump.

Stop baths are reusable. Many have indicators in them to tell you when they are used up. Usually yellow/purple. It starts out yellow then turns purple when it's used up.
"If it's yellow, then it's mellow. If it's blue, then it's through."

Fixers are usually reusable. Again, the manufacturer will tell you.
A good rule of thumb is to put some film in a fresh solution of fixer and time how long it takes to completely clear the film. Remember that time. Then, when the time it takes to clear the film gets twice as long as it did, originally, it's exhausted.
Store it away until you can dispose of it properly or, better yet, recover the silver first, then dispose.

Other solutions like wash agents, wetting agents and fixer neutralizers/removers vary in their reuseability. Manufacturer's instructions, again.