Similar to a brass monkey - the brass buffalo is a beverage made by taking several sips of beer and then mixing in several squirts of Heinz yellow mustard into it. It originated on nut farms in the countryside of the pacific northwest and is considered a delicacy.
When a dude is sitting on a small toilet seat and has to pull his twig and berries forward so they don’t fall in the toilet bowl while he’s taking a shit.
Mike had to Reverse Buffalo Bill himself so he could use the toilet on the houseboat.