Welking is the act of wiping one's anus after defecation. Specifically, it refers to a forceful act of wiping that will result in tissue paper being forcefully dragged across the sphincter itself, rather than being lightly teased across the ass-pubes. Welking may be accomplished by using two sturdy fingers, and can take the place of showering after a nasty deuce.
"Johnny, did you remember to welk after you went #2?"
"Dude! do you smell that? something smells RANK! I bet one of you guys forgot to welk!"