Trapway
From Toiletpedia
The channel in a toilet that connects the bowl to the waste outlet. Also called the colon, the S-shaped ‘trap’ curves up and then down, like an elbow behind the toilet. It is called a trapway because it "traps" downstream sewer gases behind the water that remains in the bowl between flushes.The trapway is measured in terms of the largest diameter ball that can pass through it, called a ball-pass or ball-passage.
Also See:
Images:
Concealed Trapway One Piece Toilet 1
Visible Trapway Two Piece Toilet
Toilet Diagram- from renovation-headquarters.com
