INTRODUCTION

Since its invention in the late 1800's, the siphonic flush has been the dominant toilet flush technology used in the United States and Europe. During the 20th century, the toilet was engineered to use progressively less water. Flush volumes declined over time in the U.S. from more than 7 gallons in early models, to five gallons per flush for much of the mid-20th century. By the 1980's, the standard in the U.S. was 3.5 gallons per flush. Starting with Massachusetts in 1989, some states and communities in the U.S. began requiring 1.6 gallon toilets in new construction and by 1992, 1.6 gallons per flush was the standard nationally.

Since 1.6-gallon, low-consumption(1) toilets started being produced in the U.S. in the late 1980's, there have been anecdotal reports of problems with their functioning, including a need for multiple flushes to clear the bowl and frequent clogging. With improved technology and further research into toilet design, low-consumption toilet performance has improved since the first low- consumption toilets. However, the reputation for the functioning of low-consumption toilets is based largely on experiences with early models, produced a couple years before and after the national low-consumption standard was set.

More anecdotal evidence suggests that the functioning of these early low-consumption toilets has continued to decline as they age. Research on the functioning of these aging low-consumption toilets in homes can serve as a starting point for discussion of the extent of the problem, especially the decline in performance due to aging and replacement of parts.

1. Low-consumption toilets have been commonly referred to as ultra-low-flush (ULF) toilets. The term low-consumption is used here because it is the term used when creating the 1.6 gallon standard.

Achieving the 1.6 Gallon Flush

Some of the problems with the functioning of low-consumption toilets can be traced to the ways manufacturers chose to achieve a 1.6 gallon flush. When the National Energy Policy Act was reauthorized in 1992, the American Society of Mechanical Engineers/American National Standards Institute (ASME/ANSI)(2) standards for 1.6 gallon toilets were adopted by reference, establishing them as the standards across the U.S. The ASME/ANSI standards require that toilets must flush with an average of 1.6 gallons on 5 test flushes, with none of the flushes exceeding 2.2 gallons. The manufacturer must decide how to achieve the standard.

Most manufacturers kept the 3.5 gallon tank to provide the head for a forceful flush, but adjusted the inner workings of the toilet to achieve a flush volume of 1.6 gallons. The two most common ways to achieve the smaller flush with gravity models were to use an early-close flush valve flapper or to install a toilet dam. Other manufacturers chose other options, such as pressurized flush technology or low-capacity tanks with standard flappers.

2. ASME is the author of plumbing standards published by ANSI.

Flush Valve Flappers

The flapper is the rubber or plastic piece that closes the hole (flush valve) through which water flows from the tank to flush the bowl. Standard flappers are designed with air in a bell on the inside so that they will float and close only after the water level has declined enough to seat the flapper on the flush valve. In early-close flappers, a hole is built in the flapper to allow air trapped in the flapper bell to escape early and close the valve before all the water escapes the tank. These early-close flappers are set to allow only 1.6 gallons to flow from the tank into the bowl, instead of the full 3.5 gallons.

Of the low-consumption toilets in this study, one manufacturer, Universal Rundle, chose to use a standard flapper as the flush valve. Toilets made with this design did not use an early-close flapper or a toilet dam to achieve a 1.6 gallon flush. Instead, other modifications were made to the toilet, including using a smaller trapway and a steeper bowl. These toilets use a smaller- capacity tank than most models of toilets in this study, and are generally believed to be more difficult to modify to increase the flush volume.

All flappers inevitably deteriorate over time and must be replaced. While the normal life of a toilet is at least 20 years, the life of a typical flapper under “normal wear and tear” is about five years (MWD 1998). In effect, this means that correct replacement flappers would need to be purchased three times over the expected life of the toilet.

Most early-close flappers can be replaced by standard floating flappers. Customers who are unaware that their toilet has an early-close flapper can unwittingly erase the water savings by replacing a worn-out flapper with a traditional flapper. Identifying an early-close flapper is difficult because they usually are not marked as such and attach to the toilet in the same manner as a traditional flapper. If a traditional flapper is used, the flush volume immediately reverts to the full amount of water held in the tank (3.5 gallons) and the customer may not notice any difference in performance of the toilet. Most hardware and home improvement stores carry only traditional flappers, with customers in need of an early-close flapper having to call the manufacturer to get a suitable replacement.

In addition, the quality of water used in toilets can accelerate deterioration of flappers. Use of bowl cleaners installed in the tank to constantly clean the bowl can lead to rapid deterioration and warping of flappers if the cleaner is a halogenating compound(3). Accelerated testing done by the Metropolitan Water District of Southern California (MWD) on flappers available in 1994 showed that halogenating bowl cleaning solutions could deteriorate all flappers. Since then, manufacturers have continued to improve the compounds used in constructing their proprietary flappers, and MWD tests on 1998 flappers showed that some new flappers appeared to be either not affected, or much less affected by halogenating bowl cleaners, when compared to effects shown in the 1994 testing.

High concentrations of chloramine, a residual disinfectant used in some water systems, have also been shown to deteriorate rubber toilet parts such as flappers. Chloramine was used to provide residual disinfection in Central Arizona Project (CAP) water delivered to more than half of the City of Tucson Water Department’s (Tucson Water) customers from November 1992 to November 1994. Since CAP water deliveries were discontinued, the City of Tucson has switched back to chlorine as the disinfectant.

3. In-tank bowl cleaners can consist of halogenating or non-halogenating compounds. Cleaners with halogenating agents generally use either mixed halogenated methyl hydantions or calcium hypochlorite. The non-halogenating type uses detergent and is not known to cause flapper deterioration (MWD 1998).

Toilet Dams

A toilet dam is a plastic bucket or barrier 3 to 4 inches high surrounding the flapper valve in the bottom of the tank. A standard floating flapper and a 3.5 gallon tank are used. When the toilet is flushed, the water outside of the dam and below its top is retained in the tank, maintaining hydraulic pressure to create a more forceful flush, but allowing only 1.6 gallons to be used.

Toilet dams can be easily disabled, although not so easily as to be removed unwittingly. Intentional removal of toilet dams could be prevented if they were cast as part of the tank.

Pressurized Flush

Some manufacturers use pressurized flush technology to achieve the 1.6 gallon flush. The most common of these technologies is the pressurized flush system, with a sealed air bladder contained in the tank using water service pressure to achieve a forceful flush. Pressurized flush toilets are often among the most expensive toilets on the market ($200 - $300) and can be expensive to maintain because parts are more specialized. They are also known for producing a noisier flush accentuated by a rapid flush cycle.

Other Proprietary Mechanisms

Another flush mechanism utilized in achieving a 1.6-gallon flush is the proprietary tube and bell mechanism used by Mansfield in the Allegro model toilet. Mansfield originally licensed the toilet design with the tube and bell mechanism from a Swedish company - Ifö-Sanitar, and later incorporated the mechanism in its Allegro model. In this toilet, a rubber bell slides up a tube to flush and slides back down to close the valve.

Replacement assemblies for this flush mechanism are available from some hardware stores. Both the 1.6 gallon flush and 3.5 gallon flush mechanisms are available and both can be installed in 1.6 gallon toilets. Inadvertently buying the wrong assembly from the hardware store is not likely because the packages are labeled according to flush volume, which is not generally the case with flappers. The 1.6 gallon version of this flush mechanism also could easily be modified to close later with a greater flush volume, but this would require intentional modification. The rubber gasket around the bottom of the flush valve that makes a seal with the bottom of the bell is reported to be the most common piece of the flush valve to wear out, and is also available at some hardware stores.