Concealed Trapway
From Toiletpedia
The elbow curve visible on the back of most toilets is called the trapway. Some toilets are designed so that the trapway is not visible, creating a smoother profile that is easier to clean and visually appealing.
Also See:
Images:
Concealed Trapway One Piece Toilet 1
Concealed Trapway One Piece Toilet 2
Concealed Trapway One Piece Toilet 3
Concealed Trapway One Piece Toilet 4
Visible Trapway Two Piece Toilet
Toilet Diagram- from renovation-headquarters.com
