On selenium toning, I process my prints in the following manner beginning with development:
Develop for 2-3 minutes
Stop bath for 30 seconds
First fix 4 min
Second fix 4 min
Kodak Rapid Selenium Toner (dil 1-9) for 3-4 min.
Wash for 1 hour
I found years ago that washing after last wash before toning brought on stains. When I come directly out of the last fix into the toner the problem is eliminated.
Some recommend mixing selenium toner with hypo clearing agent. This wastes toner and is counterproductive, in my opinion, since KSRT has hypo as one of it's ingredients.
I save the toner for reuse later and replenish this solution with KSRT as needed.