When, during anal sex, the penis(s) penetrate the anus so hard that shit blasts out of the anus. May also lead to an anal rupture.
Guy: EWWW!!! WHAT THE HELL WAS THAT??
Girl: Umm...I think I just had an anal waterfall....go slower next time.
Girl: Umm...I think I just had an anal waterfall....go slower next time.
by SaintCoolio June 2, 2010
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