Dump and Stack

When a person gets on a toilet to defacate, only to be sat on top of by another person who defacates between his or her legs. There are three variations: standard, where both people face forward; the side-saddle, where the top person sits like a child on Santa Clause's lap; and the reverse, which allows the two people to make out with each other while defacating.

A dump stack is achieved by eating a meal that pushes out a lingering dump in your innards. The pressure on the existing dump caused by the ingestion of the meal gives the push needed to clear things out.