I'll reuse it for one session (usually 3 or 4 rolls of film) then dump it.
I mix it with an eyedropper. I have a spare film canister that I don't have a lid for. I fill that with clean water then drip in a few drops.
I have occasionally forgotten to dump it out after I'm done and discovered it when I go looking for my spare to mix up a new batch. I have reused it with no problems.
The stuff is so cheap and you use so little of it per batch that you can just dump it out.
I'd say it's worth it just to prevent the risk of cross contamination.