I've used the Tetenal 1 litre kit and I have processed 12 rolls of film (120 and 35mm) without replenishment or increased development times (assuming no 400 iso films which deplete the chemicals at a higher rate thus reducing the total number of rolls). So, to answer your question, if you have reached the development capacity of your chemicals, you should dispose of them the way you dispose your b&w chemicals. For me, I store my spent solutions in a 5 gal container and every 6 months or so take them to my community for environmentally correct disposal.