Water enters through diagonal punching around the rim of the bowl, creating a vortex that draws the water down into the rear trap with a swirling action that scours the walls of the bowl. Water strikes two parallel ridges and folds over forming a jet, producing siphonic action. Large water surface provides a very efficient and clean process, and the flushing is extremely quiet. This model is mostly of one-piece construction with a low profile. Expensive.
Water enters through rim punchings and jets placed in an up-leg of the rear trap, filling the trapway and creating an instant siphon action without rise of water level. The result is quick water withdrawal. Large water surface provides an efficient and clean operation. With quiet flushing and moderate cost, this is the most popular residential model.