What is the name of this model?

The correct answer to this question is SIPHON-JET. A siphon jet is a pocket which is molded. It appears in front of the toilet and holds extra water. It will keep this water until the toilet is flushed. Siphon jets point into the trap way.

Once the toilet is flushed, the action of the vacuum pulls the water that was stored out of the siphon jet pocket. This action increases the power of the flush. Although not yet found on all toilets, it is becoming widespread to find on most modern toilet systems. Companies such as Toto and Kohler use the siphon-jet on their models.