Jim flushes the Snix mask down the toilet at the end of the movie; it would physically be impossible to flush a large piece of paper in this case as it would clog the plumbing. The sewage treatment system can handle the flushed paper, although they don't want people to deliberately flush trash - because it unnecessarily increases the burden on the system.
At some points in the movie, Brian Genk and James Rolfe corpse (break character by laughing).