How does a vampire with “Methuselah’s Thirst” get full?

The Feeding flaw “Methuselah’s Thirst” on page 181 says “Your hunger can only be fully slaked by the blood of supernatural creatures…otherwise, it remains constantly at a minimum of 1.”

Does this replace the usual rule where the only way to “fully slake” hunger is to drain and kill a human being? (p.212) Do they stack? If so, is your hunger dice floor at 2 until you find someone supernatural to drink from? Or do you have to drain a supernatural creature to death to lose your last hunger die?