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Can Your Plumbing System Handle a Low-Flow Toilet?

Low-Flow Toilet

Water-saving flushers can save hundreds of gallons of water over their lifetime, but only if your plumbing system can handle the switch in fixtures.


Low-Flow Toilets Could Be a No-Go

Builders of older houses assumed toilets would always flush more than 3 gallons of water to carry away waste, not the misery 1.6 gallons today’s toilets use. So there’s a chance that plumbing in an older home simply can't work with that relative trickle.


Pipe Slopes Can't Cope

Waste drains beneath the toilet need to slope between 1/8-in. and 1/4-in. per foot for the water to carry solid waste to the sewer. If they’re too steep or too level, the flow of water allows waste to collect in the pipe and that means clogs. Some old houses, for reasons of age or builder error, may even have a “negative slope” where water stands in the pipe. Waste is carried away only by the force of gallons of water flowing through the system courtesy of an older toilet.

Don’t be too worried, though. The average home plumbing system will work fine with today’s low-flow toilets. Just watch out for a couple of danger signs:

  • The original toilet backs up occasionally, even when solid waste isn’t being flushed. The problem may be caused by a clogged waste line rather than the toilet itself.
  • After lifting the toilet off the floor for other maintenance, you shine a flashlight into the drain and discover standing water in the waste line. Even if it’s just a little, that’s a warning sign the system has developed a negative slope.
  • In either case, you’ll need a professional plumber’s services to correct the problem. If your plumber says the line may or may not work for a low-flow toilet, consider installing a fixture with a pressure-assisted flush. These use water pressure to charge a compressed-air tank inside the toilet tank. When flushed, they release the compressed air to drive water out of the bowel fast, forcing it down the drain and into the main sewer stack quickly enough to carry off solid waste.

Whatever new toilet you choose, look for one carrying the WaterSense label. These typically are 20 percent more water-efficient than average products in their category. What does that mean to you? The U.S. EPA calculates that replacing a single pre-1980 toilet with one measuring up to WaterSense standards can save an average family 18,000 gallons of water and $110 in utility costs.

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