How does the conversation about "the age of disposable tissue"(from Clarisse's house)relate to the events in Montag's house a few moments...

After Millie Montag gets her stomach pumped and her blood
replaced, Guy leaves the house and goes over to the McClellans' home.  He hears the
words you mention.  To me, they apply to what has just happened at his house in a couple
of ways.

First, something that was part of Millie has just
become, quite literally, disposable.  The men are taking away Millie's blood (as well as
the contents of her stomach) and will presumably throw it away.  This shows how much
people have lost their humanity -- their very blood has become
disposable.

Second, you can say that Millie herself is
disposable.  It's like she does not even care about herself anymore.  She no longer
thinks of herself as something important.