Keli Sheni Follow-Up

Question

The Rav was recently asked: "Is it true that it is technically unnecessary to use different plates and utensils for pesah because the majority of their use is for kli sheni?" The Rav answered: "Anything that is normally used as Keli Sheni does not need Hagalah. Yes. It's right there in the Shulchan Aruch...." 1) Please provide the source in the Shulchan Aruch. 2) If this is the case on Pesach when we are even more stringent with kashrut, is it necessary to have a seperate set of dishes for meat and milk anytime during the year if they are all keli sheni? 3) Does it matter whether the dishes are pottery, china (glazed), glass or metal? 4) If so, what are the differences? 5) Is it necessary to have a seperate set of silverware anytime during the year if they are all keli sheni? 6) If we are permitted to use one set of dishes and one set of silverware but we choose to keep two to be stringent, why must we do seperate milk and meat runs in a dishwasher?