Stop bath is exhausted when it is purple. Fixer remover is exhausted when it is not blue anymore. Sodium sulfite is exhausted when it is dark pink and mucky. Sepia toners These chemistries may be flushed down the drain with plenty of running water to dilute the concentration and to clean the sink.
Silver is removed from paper and film in the fixing process and is collected in the fixer.
Heavy metals, by law, may not be dumped into the water supply. The fixers are monitored and treated properly by the staff. Keep the trays covered when not in use so that fumes and vapors are kept to a minimum. Like silver, it is a toxic heavy metal. It is stored in a closed labeled container when not in use.