Toilet Technology

Gravity-fed toilets

Gravity-fed toilets are the most common type installed in private homes. As the name implies, gravity-fed toilets rely on gravity to flush waste. When the handle is pushed, a flush valve opens, and the water in the tank drains into the bowl. The water pulls waste through the toilet’s trapway and into the drain.

How a Gravity Toilet Works

Pushing on the handle pulls the chain, which releases the stopper.
About 1.28 – 1.6 gallons of water from the tank is released into the bowl.
When the trapway fills with water, a siphon is created that pulls the waste out of the bowl.
Meanwhile, when the level of the water in the tank falls, so does the float. The falling float turns on the fill valve.
Water flowing through the fill valve refills the tank as well as the bowl. As the tank refills, the float rises, and shuts off the fill valve when the tank is full.

There are different types of gravity-fed toilets, using varying amounts of water to flush waste. Dual-flush toilets, for example, have been available in Europe for a number of years, but they’re fairly new to the North American market. Dual-flush toilets let users choose from one of two flush options depending on need: Users can push one button (or pull down on the handle, depending on the toilet style) for a regular 1.6-gpf flush, or they can push another (or push the handle up) for a reduced flush using about 1.1 gallons of water. Based on user studies, dual-flush toilets used correctly comply by achieving an average flush volume of 1.28. This translates into one full flush, for every two reduced flushes.

Pressure-assist toilets

Pressure-assist toilets are suitable for any installation where tank-type toilets are required, including offices, buildings, restaurants and residences. The system uses line pressure to create a pressurized flush, which, in turn, pushes the waste out of the bowl. Each technology is only available with specially designed bowls. This is why pressure assist and gravity are not interchangeable.

In comparison to gravity-fed toilets, which pull waste through the system, pressure-assist toilets use a forceful pushing action. This pushing motion is enabled by a special pressurized vessel technology that replaces the gravity toilet-style tank.

How a Pressure-Assist Toilet Works

The pressure-assist system traps air as the vessel fills with water.(1)
The water supply line pressure compresses the trapped air inside the vessel. The compressed air is what forces the water into the bowl, so instead of the “pulling” or siphon action of a gravity unit, the pressure-assist unit “pushes” waste out.(2)
The vessel refills and begins the cycle again.(3)

STEP 1. Water Flows To Vessel		STEP 2. Vessel Ready To Flush		STEP 3. Air Pressure Empties The Valve

High-Efficiency Toilets: Less Water = More Savings

Current federal law limits the allowable amount of water used to flush a toilet to 1.6 gallons per flush (gpf). Although some models in the first generation of “low-flow” toilets performed poorly, and consumers wondered if 1.6 gallons of water wouldn’t be enough water to sufficiently move waste through the drainlines and into municipal sewer systems, homeowners should not let these outdated fears impact their decision about installing water-efficient toilets. In fact, some of today’s low-flow toilets are highly rated in terms of flushing performance.

Look for this in the Future!

Manufacturers have made such great advancements in toilet technology that they’re now delivering toilets that use less water than ever before. Today’s high-efficiency toilets (HETs) go beyond the 1.6-gpf standard and use less than 1.3 gpf. The U.S. Environmental Protection Agency’s voluntary WaterSense program includes a label for using on HETs that are certified by an independent laboratory test, which has rigorous criteria for both performance and efficiency. Only HETs that complete the third-party certification process can earn the WaterSense label.

According to the EPA, a WaterSense-labeled HET can save 4,000 gallons of water per year. If a family of four replaced a 3.5-gpf toilet made between 1980 and 1994 with an HET, they could save more than $90 annually on their water bill, or about $2,000 over the lifetime of the toilet. These savings mean that a new WaterSense-labeled HET can pay for itself in only a few years. Additionally, some local utilities across the U.S. offer rebates, ranging from about $25 to $175, for replacing old toilets with HETs.

Although 1.28-gpf gravity-fed models are just emerging on the U.S. market along with the dual-flush toilets, 1.0-gpf pressure-assist toilets have been available since 2004. The vigorous flushing action of the pressure-assist technology, along with the larger, glazed trapway of the toilet, enables pressure-assist models to operate very effectively with only 1 gallon of water. Consumers don’t have to accept any toilet performance sacrifices to be good environmental stewards!