Today's water-conserving toilet is designed to flush with only 1.6 gallons of water. While this is an improvement over older toilets that need 3 to 7 gallons per flush, it also means that each flush must push an average of 500g of human waste through the sewer line. To determine the best flushing toilets, in 2003, the Alliance for Water Efficiency created Maximum Performance Testing guidelines (MaP) to help reviewers rate toilets.
Using MaP guidelines, The Alliance for Water Efficiency rated more than 1,700 toilets. Testers flushed simulated human waste made from an encased mixture of soybean paste down each toilet in increments of 250g up to a maximum of 1,000g. Toilets received high ratings based on the highest mass of waste they could dispose of in one flush. Eighty of the best flushing toilets are listed in a report available through the organisation's website (see Resources).
Gravity Flush Toilets
Gravity toilets work when the tank releases water and forces the trap open. The force of the water flushes waste through the toilet's 2-inch line into the drain. Gravity toilets work better with more water. Since newer toilets are required to flush with 1.6 gallons of water, toilet manufacturers such as Toto and Kohler have incorporated G-Max technology. G-Max technology angles tank water directly over the bowl, which increases the pressure on the trap and forces waste down the drain. Toto's Drake and Ultramax models were highly rated for their ability to flush 900 grams of simulated waste in a single flush. Kohler's Cimmaron, a toilet with an elongated bowl design, flushed 1,000g of waste in a single flush.
Pressure Assist Flush Toilets
Pressure-assist toilets simulate the action of an aeroplane toilet. Water held under 11.3 Kilogram per square inch (psi) fires out of the tank and catapults waste and toilet paper through the toilet drain. As a flush method, while loud and startling, pressure-assist flush technology is highly effective, especially if your home has low water pressure. Model's such as Gerber's Ultraflush and the Purist Hatbox received high marks for flushing 800g of simulated waste in a single flush.
High Efficiency Toilets
High efficiency toilets (HETs) use less water than standard 1.6-gallons-of-water-per-flush (gpf) toilets -- many use 1.28 gallons or less. In fact, HETs with the EPA's WaterSense label are certified to flush 350g of solid waste per flush with only 1.28 gallons. Several hundred toilets qualify for the WaterSense label. In fact, manufacturers such as Toto, American Standard and Koehler put out HETs that flush up to 1,000g of solid waste. While more expensive than standard toilets ($500 as reported April 2010), the savings in water may be made up over the course of a year.
Dual Flush Toilets
Dual-flush toilets utilise different tanks and water amounts for solid and liquid waste. Two buttons located on the tank cover control the type of flush. While the solid waste side releases 1.6 gallons of water, the other button releases a mere gallon for liquid waste. Gerber, Mansfield and American Standard all produce highly rated dual-flush toilets that successfully pushed 1,000g of simulated waste in the first flush. In fact, TerryLove.com rated the Gerber dual-flush toilet as one of the best toilets on the market.