A nasal bucket refers to a bucket bong (AKA gravity bong) used for inhaling THC, but through the nostrils. This is perhaps the most potent form of marijuana inhalation. Because of this, people often make bets, where the loser must take a nasal bucket. If you are willing to wager a nasal bucket that you are right, you are said to be Nasal Sure.
Felipe: Chris Rock was funny in "The Nutty Professor".
John: Chris Rocks wasn't in that movie.
Felipe: I'm sure he was.
John: Are you nasal sure.
Felipe: Hells yeah
Dave: I'll set up the nasal bucket. Felipe's about to get fucked.