The liquid which appears during toilet backwash. Carries with it an awful and awesome smell that can eliminate a grown man. Can often be placed into normal conversation to add hilarity unknown to bystanders.
Tramp: "Can I have a wee bite o yer sandwich?"
Lewis: "Yeah, it's a bit bumwee though. Thats a nice bumwee you've got."
Tramp: "Is yer friend takin' the piss?"
"My GOD! It smells like bumwee in here! The smell is like getting hit in the face. WITH A SHIT!"