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1.
To flush the toilet first in order to drown the sound of your farts and diarrhea. People who preflush usually shit during the flushing noises.
1. The dude in the stall next to mine was preflushing so that people wouldn't hear his violent diarrhea.

2. I had to preflush right before I let out a loud fart while taking a dump.
by JayZed April 27, 2010