Clarification

Question

I looked at some of my kashrut books and I don't understand why you said that if there is meat on the sponge, it doesn't transfer taste because it is a keli sheni. What is the keli sheni? Also, it would seem that it doesn't transfer taste because the hot water coming from the spout is iruy keli rishon and even though iruy can cause a taste transfer into food, it cannot cause a taste transfer into a utenssil. I wonder why you didn't give this as the reason. Is it because not all poskim accept this?