Plumbing Info

by Mike McClintock – October 14, 1999

Homeowners have talked about the problem of low-flush toilets since 1992, when the U.S. Department of Energy mandated them as a water conservation measure. The units are about the same size as older designs but use about half the water–1.6 gallons instead of 3.5 gallons per flush–and consequently have less flushing power. It’s not a common subject in public conversations, but in private, the general consensus has been that low-flush units are one of the most troublesome components in new and remodeled homes.

Those opinions have been confirmed by a nationwide survey of 1,270 builders and homeowners conducted this summer by the National Association of Home Builders Research Center. It found that roughly four out of five people experienced problems with low-flush units in the past year. A majority of the builders reported problems from more than one of their clients, and many reported hundreds of problems. Most builders surveyed also said that they receive more callbacks on low-flush toilets than on anything else.

There are four common complaints: multiple flushes are needed to clear solids from the bowls; residue remains in the bowl even after multiple flushes; the units clog easily; and they require more maintenance than 3.5-gallon models and cause more damage when they overflow. And unlike other problems that turn up even in well-built houses, most builders and homeowners say that the toilet trouble can’t be fixed-but not for lack of trying.

In the typical scenario, homeowners jiggle the handle, try to increase the flow at the water supply valve and attempt other fixes that have no effect. A few contact toilet manufacturers about the problem. Most complain to their builder and point to inadequate water pressure or substandard plumbing work, and characterize the fixtures as inferior or cut-rate products as evidenced by poor performance.

Builders report that most clients do not accept the explanation that the toilets are working, and can’t be replaced with ones that use more water and work better because they are against the law.

Although recently manufactured low-flush units perform better than the earlier models, many builders said, the NAHB survey found that 60 percent of builders and 28 percent of homeowners experienced so much trouble that they contacted plumbers in what they described as futile attempts to solve the problems. While many of the reported service calls were under $200, about 9 percent cost up to $500 and more to deal with damage from overflows.

In the end, homeowners are left to cope as best they can with the problems. Some try to adjust the fill mechanisms to increase the water in the holding tank. Most resort to double flushing, which defeats much of the water-conservation potential of low-flush systems. This tactic may skew many of the surveys that show how much water low-flush units can save.

Data collected on a sample of 1,188 North American single-family homes last year by the American Water Works Association found significantly less water use in homes with low-flush toilets and other conserving fixtures such as low-flow shower heads than in homes without these fixtures. The non-conserving homes used 73 gallons per capita per day, with 20 gallons, or 26 percent of the total, for toilets. The homes with water-conserving fixtures used 50 gallons per capita per day, with 10 gallons, or 20 percent of the total, for toilets. Replacing conventional toilets with low-flow models has the potential to save up to 12,000 gallons a year in a typical household. But the savings can be accompanied by ongoing aggravation and recurring expenses from stoppages and overflows. And in practice, given the widespread practice of double flushing, the savings are likely to be less dramatic. If you have a say in the matter, there are three basic types of low-flush units to choose among, although one is largely commercial.

* Gravity-tank toilets, the most common and inexpensive, have a bowl and a tank, and depend on the volume of water in the tank to flush wastes. In theory, they require water pressure of 15 pounds per square inch (psi).

* Pressure-tank toilets, the other residential alternative, look like gravity models but have a secondary container inside the tank. It uses the pressure of water coming into the main tank to compress air trapped in the inner tank. Each flush is pressure-assisted to push out wastes instead of pulling them out with the siphon action of a gravity unit. This hybrid design usually operates with 25 to 35 psi of water pressure (at the toilet) and is roughly twice the cost of basic gravity units.

* Flushometer toilets, typically used in commercial buildings, have no tanks and are flushed with a hand level at a pressure-sensitive valve. They also depend on water pressure to flush wastes but usually operate with higher water pressure.

Major remodeling of existing bathrooms can cause even more problems than new construction because drainage plumbing in some older houses is designed to work with a higher flow rate. It’s possible that with low-flush fixtures, water pipes leading to the sewer could become clogged over time if the water flushing through them is too scant or not forceful enough.

If you have had intermittent drainage problems in the past, installing a low-flush unit will probably make them worse. This design dilemma drives some homeowners to recycling yards and restoration suppliers in search of older toilets, no matter what their style.

Thursday, October 14, 1999 – page T21 – Copyright © 1999 The Washington Post Company


  1. Nicole

    Good to know. I’ve never experienced residue with a low flush toilet until we bought our second home. It looks gross but the residue is just in the very bottom of the bowl. I don’t care except when we have guests. I don’t want them to think I don’t clean my toilet but I could clean it every morning and the residue will come right back after anyone goes number 2 and some of it doesn’t scrub off cuz of the brush I have. But knowing another toilet won’t help relieves some stress. I didn’t want to spend money on another toilet so thank u

  2. herman

    I have a Delta toilet , when it is flushed it leaves poop on the side of the bowl. It is a low flush toilet with an elongated bowl, any ideas?

  3. Ralph Robinson

    After flushing the bowl fills correctly but after about 45 min the bowl is empty leaving just a little water in the very bottom. What is causing it to siphon the water out.

  4. Marc Blissett

    Wish I had read this article prior to remodeling my cabin. Now with the low flow model my line to the septic tank gets clogged easily. We need to used a 5 gallon bucket of water once week to keep it cleared out. Never had an issue with the older high flow toilet.


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