1.6 Gallon, Low-consumption Toilets

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There are a number of factors that play into how well the low-consumption toilets work -- the size of the drain; the design and shape of the bowl, the tank and it's fittings; how often they are used; their location in relation to the other fixtures in the bath as well as the house, etc.

Seattle plumber Hill Daugherty says, "houses that have 4-in. to 6-in. cast-iron drains are a problem. When you put a 1.6-gal. toilet in with that diameter pipe, it just barely makes the bottom of the pipe wet. As a retrofit in a house with old plumbing, it's lousy. Now I run high-use fixtures, like the washing machine, just after the toilet. The washing machine will help move that waste down the line." Washington, D.C., plumber Ken Goldman believes that retrofitting 1.6-gal. toilets is the biggest source of problems plumbers have with the new fixtures. "We're using plumbing fixtures designed for the 1990s and putting them in plumbing systems designed for the 1920s," Goldman said.

Testing Toilets for Drainline Carry

Evaluation of Water-Efficient Toilet Technologies to Carry Waste in Drainlines

This 40 page report was initiated by municipalities and other interested organizations in Canada, the Drainline Carry Testing program was a cooperative effort between Canada Mortgage and Housing Corporation (CMHC) and several Canadian partners.

To establish a relative ranking the carry distance of each flushing system was compared to the average carry distance of all models tested. The 6-L pressure-assisted model achieved the highest ranking with carry distances approximately 130% of the average distance, whereas the washdown and vacuum-assisted models had carry distances of less than 80% of the average. Study results showed a modest relationship between flush rate (how quickly waste is evacuated from the bowl) and drainline carry. For example, the 3.8-L pressure-assist model (quick flush rate) flushed with only 63% of the water and carried waste 71% as far as the average nonpressure- assist 6-L model, but the flushing systems that scored second and fourth place overall are both gravity models using traditional 50mm (2 inch) flappers (relatively slow flush rate).