Slope, toilet paper critical to drainline carry

Nov. 28, 2012
The slope of the drainline and the wet tensile strength of the toilet paper are the two most important factors affecting drainline carry in commercial plumbing applications, a study has found.

CHICAGO — The slope of the drainline and the wet tensile strength of the toilet paper are the two most important factors affecting drainline carry in commercial plumbing applications, a study has found. The Plumbing Efficiency Research Coalition (PERC) announced that its long-anticipated study, “The Drainline Transport of Solid Waste in Buildings,” has been released and is now available on the PERC Website:

PERC was formed in 2009 by a coalition of interested parties, including contractors, manufacturers, engineers, and code officials, because of the increasing use of low consumption water closets in commercial spaces that may have long drainline runs and few ancillary flows, such as showers, to transport waste down the pipe.

PERC was formed in an effort to meet the critical need for information on this topic. On Jan. 5, 2009, at the U.S. EPA offices in Washington, a Memorandum of Understanding (MoU) was executed among five plumbing and water efficiency associations constituting PERC: Alliance for Water Efficiency, International Association of Plumbing & Mechanical Officials, International Code Council, Plumbing-Heating-Cooling Contractors – National Association, and Plumbing Manufacturers International. In 2011, the American Society of Plumbing Engineers joined the coalition as its sixth member.

Since PERC was founded in the depths of the recession, it became clear that no federal grant money would be forthcoming; all of the research was funded by industry and concerned parties. PERC took pains to thanks all of its benefactors, especially American Standard, which set up the test apparatus at its Product Development Design Center in Piscataway, N.J.

To approximate the kinds of distances encountered in commercial applications, the test piping, made mostly of clear 4-in. PVC sloped downward for 65-ft., took a wide-sweep 90-degree turn for 5-ft., took another wide-sweep 90-degree turn and continued for an additional 65-ft., or 135-ft. total.

Researchers made clear that this was not another toilet test, so the apparatus does not use a toilet. Researchers devised a “surge injector,” a manually operated, valved length of pipe that installs on top of the closet flange on the test apparatus. The surge injector can be loaded with the test media, squares of toilet paper and 50-gram soybean paste faux feces, along with water. The surge injector is “flushed” by manually opening a valve. The device is also rigged so that researchers could mimic the effect of toilets that use either more or less trailing water in a flush. (Ultimately, percent of trailing water turned out to not be a significant factor.)

The surge injector is filled with amounts of water to mimic flushes of 1.6-gal., 1.28-gal., 1.0-gal., and 08.-gal., matching the type of toilets that are on the market today.

Drain piping on the test apparatus can be sloped at either 1% or 2%. Researchers found that slope was the most significant variable in drainline carry, with 2% being better.

In consultation with C.J. Lagan, American Standard’s manager of compliance engineering, researchers created a Design of Experiment that uses a statistical tool called Analysis of Variables or ANOVA. ANOVA is used to separate random occurrences — noise — from statistically significant results. The testing discovered that the results of flushing using 0.8-gal. was so variable and unpredictable that it was deemed to be noise and the 0.8-gpf. tests were not included in the data.

PERC took note of previous research published abroad that pointed out concerns that needed additional research. In a study by Dr. Steve Cummings, Research and Development Manager, Caroma Dorf, and manufacturer co-chair of the Australian coalition, ASFlow, committee, the results revealed that selection of toilet paper (and its wet tensile strength) had a profound impact on drainline transport distances. Higher strength paper resulted in shorter transport distances. As a result of ASFlow findings, a simple test was developed by the PERC TC to roughly measure the wet tensile strength of toilet paper available in North America. The wet tensile strength test was then used to select a high tensile strength toilet paper for use as a “worst case” selection for the PERC Test Plan.

The toilet paper test is simple. A sheet of toilet paper is rubber-banded to the opening of a plastic cup, and then soaked in water for 60 seconds. Quarter-inch steel washers are then placed on top of the toilet paper until it breaks and the number of washers counted. The wet low tensile strength toilet paper only held one washer. The high tensile strength toilet paper held 82 washers. It became quickly apparent to the researchers that users would use much more of the low tensile strength toilet paper, so the test used 48 sheets; tests with the high tensile strength toilet paper used 24 sheets.

Researchers acknowledged that in the real world, building drain slope will be somewhere between 1% and 2% and the toilet paper used will fall somewhere between the best case and worst case examples used in the test. They are, however, the first factors to consider in commercial buildings experiencing clogging problems.

The volume of water flushed ranked as the third most significant factor in drainline carry, especially after the 0.8-gpf results were removed from the data. The last two factors, percent of trailing water and flush rate (i.e., toilet flush discharge characteristics) were deemed to be insignificant.

Researchers tested the concept of a “clearing flush,” 5-gal. sent down the drainline periodically to clear out waste products. The clearing flush failed to clear the drainline in seven out of 39 tests, so researchers deemed it to be unreliable and not recommended.

This first report is just Phase 1, PERC noted. For example, future tests should be run using 3-in. drainlines. Tests should be devised, they said, that mimic the roughness of cast iron pipe. Researchers may also want to revisit the concept of a clearing flush with different amounts of water at different intervals.

The full report is available on the PERC website at:

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