The two-piece Gerber Ultra Flush 21-312 toilet earns accolades from reviewers, who say it removes the most solid waste in a single flush. This pressure-assisted toilet uses compressed air inside the tank, which creates a turbo-charged flushing action. The Gerber also has a large water surface, which helps keep it clean and prevents stains, and though it's powerful, testers say it's quiet as well. However, bear in mind that pressure-assist toilets require home water pressure of at least 25 pounds per square inch (psi); if your home has lower water pressure, you might want to consider a gravity toilet, such as the less expensive and highly rated Toto Drake CST744S (*Est. $255).
The Gerber Ultra Flush 21-312 toilet is included in a ConsumerReports.org's roundup; this toilet is also discussed in the Maximum Performance (MaP) Testing of Popular Toilet Models 15th Edition.
ConsumerReports.org editors test the Gerber Ultra Flush and 24 other toilets using baby wipes, sponges, plastic balls and tubes designed to simulate waste.
Review: Toilet Ratings, Editors of ConsumerReports.org, August 2008
2. Alliance for Water Efficiency
In this 15th edition of the test, reviewers were given the choice of uncased media or soybean paste encased in a latex membrane "similar to a sausage" to evaluate toilet performance. The results are charted by manufacturer and toilet performance. The Gerber Ultra Flush is one of the top performers here, flushing 1,000 grams of simulated solid waste per flush.
Review: Maximum Performance (MaP) Testing of Popular Toilet Models, 15th Edition, Veritec Consulting Inc. and Koeller and Company, October 2009