Print Chemistry will only last for one day (at the longest) sitting in the trays. If the Stop Bath appears blueish, then pitch all the chemistry as that is an indication that the chemistry is exhausted. Stop bath should be yellow.
There is also a means to chemically test the fixer using some special drops, but if the stop is exhausted it usually means it is all exhausted.
If you are getting weird blotches on your prints, it is either from contaminated tongs or exhausted chemistry.
To properly dispose of spent chemistry:
The Developer and Stop Bath go down the main drain. The fixer goes down the trough on the far right of the sink which has its own drain. Rinse everything out thoroughly including the trays, the tongs, and the sink itself.
Fill the trays with pre-mixed chemistry from the tanks. If it is only you, just use 8x10 trays. If it is two or more people or you expect a number of people to use the chemistry throughout the day then use the 11x14 trays. An inch or so of chemistry should be sufficient. In any case, make sure there is plenty of chemistry in the trays to easily cover your prints.
If you are the last person printing, cover the trays with other trays flipped over in order to help keep out air which speeds the exhaustion of the chemicals.
Leave a note tape to the sink or on on the trays stating when the chemistry was placed in the trays.
Ask me or a lab tech about any questions you may have.