You really don't even have to sacrifice that much. I took probably 50mL of stop bath and slowly poured in some mixed developer until I saw a change. In my case I'm using Kodak Indicator and it turned purple. Before I did this, I was saving stop bath after printing, but dumping it when developing film. Now that I know this, I dump the stop bath from the container into a beaker. If its turned purple, I dump it. If not, it goes back into the storage container. I don't shoot or print as much as some do, but I've never actually had a batch turn yet.