FAQ’s – Phase I Drainline Transport Study Report

  1. Why did we undertake this study? Was there a specific problem we were seeing?
    Even before the Energy Policy Act of 1992 was signed into law, the drainline transport efficacy of 6.0 liter per flush (Lpf) / 1.6 gallon per flush (gpf) toilets was being debated. The U.S. is currently in another market transition towards 4.8 Lpf / 1.28 gpf toilets, reducing consumption levels by another 20 percent and many toilet manufacturers are voluntarily making toilets that flush at 3.0 Lpf / 0.8 gpf or less. The plumbing trades and drain cleaning service companies have reported increased instances of drainline blockages, but no data is available to determine to what extent this is happening. As a result, claims of increased blockages have been anecdotal, although most plumbing professionals report that these claims have merit.In addition, in Australia, where water efficiency measures have been progressing and being implemented faster than here in North America, blockages in both building drains and sewer lines are increasingly occurring.
 Recognizing that ongoing efforts to make our plumbing systems as efficient as possible , PERC sought to apply a scientific approach towards a better understanding of drainline function under lower flow conditions so that we can work proactively to prevent widespread blockages from becoming a reality.
  2. What were we hoping to demonstrate?
    By carefully controlling certain test variables, we were able to learn how drainlines react and which of these variables impact performance significantly and which variables do not. This allows us to better predict under which conditions and at which toilet consumption levels problems are more likely to occur.
  3. Why did we need a second phase of this study?
    As stated in the Phase 1 report “The work reported here, while providing significant findings, simply scratches the surface and, as with most research programs, the findings carry with them a whole new list of issues that require further investigation.” Taking into account the many drainline variables that exist in buildings in terms of materials, slope, aging conditions, quality of installation, geometry, etc., it was clear that additional work was required to fully understand the implications of reduced flows.

    Phase 2 of the study also provided clarity regarding the potential for pipe size reductions to improve drainline transport performance in long building drains. It also provided new insights on the “tipping point” where chronic blockages are likely to occur due to reduced water flows.

  4. What were the implications for the U.S. EPA’s WaterSense program for the Phase 1 Study? What about Phase 2?
    The Phase 1 report concluded that the use of 4.8 Lpf / 1.28 gpf toilets performed predictably during testing. That allowed PERC to recommend to the U.S. EPA WaterSense that their labeling specification for High Efficiency Toilets be expanded to include commercial, flushometer-valve activated models.

    While the Phase 2 Study does not include similar, explicit recommendations to the WaterSense program, it does illustrate the need for caution regarding continued reductions in toilet consumption volumes.The PERC TC is confident the WaterSense team will carefully review and consider the Phase 2 report findings as they pertain to both their existing and new specifications.

  5. Why was a 4-inch diameter drainline chosen for the Phase 1 Study? A 4” diameter drainline was chosen because the focus of the PERC drainline transport (DLT) research was on commercial installations. As mentioned in the report, the conditions we were trying to replicate with this study was a commercial office building that had no cafeteria or other water consuming features that would provide long duration flows into the building drain. Such an installation would employ 4” diameter pipe for the building drain.

    A major objective of the PERC Phase 2 study was to evaluate reducing the pipe size to 3” diameter in order to determine the significance of pipe size reduction in improving drainline transport performance.

  6. Two 90 degree bends in the apparatus don’t seem to be representative of the ‘real world’. How do you account for that?
    Nothing about the drainline apparatus was intended to be representative of the ‘real world’. This is discussed in detail in the report. Essentially, understanding that real world building drains vary so much, the PERC Technical Committee (TC) determined that the best way to approach this study was to create a near perfect building drain test apparatus and study the behavior in the apparatus under different test conditions. Regarding the geometry of the apparatus, the “U” shape was chosen as it allowed for the longest length for the apparatus that fit into the floor space available to PERC.
  7. Should PERC have used ‘real world’ pipe materials and conditions, such as cast iron (aged)?
    When one considers this issue carefully, there are many reasons why using actual aged cast iron pipe for the research is not a good idea. If we decided to employ cast iron pipe in the PERC study, it would have necessitated that the pipe be slotted at the top to allow for visual tracking of the test media during the testing. This would have created several problems, including the possible lack of structural integrity and safety concerns for the test technicians. Further, as cast iron pipe degrades, the roughness becomes extremely variable. This would have made it impossible to correctly characterize the true significance of the rough surface in the designed experiment.

    Most importantly in the ‘real world’, when considering roughness, biofilms develop quickly in sanitary pipes of all materials, negating the initial roughness of the pipe material.

  8. As I read the study, have I correctly concluded that pressure-assist toilets have no advantages over gravity fed when it comes to drainline transport?
    No. It is more accurate to state that toilet discharge velocity has no advantage when it comes to DLT. Keep in mind that one of the main objectives of the PERC studies was that we would not rank or otherwise characterize specific toilet technologies. Pressure-assist toilets, both flushometer-tank and flushometer-valve models, not only flush faster but often also tend to break up the solid contents in the bowl to various degrees compared to typical gravity toilet. This aggressive flush action might indeed have some drainline transport benefit. Determining if this is true and its relative significance would require a separate and focused study that by its very nature would rank toilets by design attributes.
  9. By conducting the testing at an American Standard facility, didn’t PERC introduce some degree of ‘bias’ into the research program?
    No. The PERC test plan did not provide a means or a motive for applying bias to the test results. It is important to keep in mind that a full product line manufacturer, such as American Standard, that manufacturers and markets all types of toilets, would gain no advantage in a particular outcome in this study. American Standard’s contributions to this effort are in the interest of advancing the understanding of how our building drains react to reduced water flows. Clearly, this knowledge benefits all industry stakeholders and, in the opinion of the PERC TC, American Standard is to be commended for their considerable financial and in-kind contributions towards this research.
  10. Wouldn’t it have been better (and more realistic) to test with real toilets rather than the surge devices?
    No. Analysis of the PERC Test Plan data relied heavily on strict control of flush discharge characteristics such as flush volume, flush rate and percent training water. Real toilets are simply not capable of regulating these attributes accurately from flush to flush. The surge injectors were much more capable of controlling these variables than actual toilets are and thereby allowed us to have a higher level of confidence in the test data.
  11. It seems that by limiting the consumer flushable materials in the test program to toilet paper, you ignored the other consumer products that are implicated in contributing to clogged drainlines. These include so-called “flushable” personal wipes, toilet seat covers, feminine hygiene products and paper towels. Will there be a Phase 3 study that includes these materials?

    At this time, PERC is not considering a Phase 3 study on drainline transport. A detailed discussion is included in the appendices of the PERC 2 report on the rapidly evolving nature of toilet paper and consumer flushable products.

    As researchers and standards developers know, any attempt to do research using propriety materials for test media is risky. Indeed, PERC almost experienced such a problem, as it was difficult to identify a toilet paper for the Phase 2 study with a wet-tensile strength comparable to the high wet tensile strength paper used in the Phase 1 study. The brand used in the PERC 1 study was reformulated by the manufacturer in the interim between the Phase 1 and Phase 2 studies to be smaller in area and had a much lower wet-tensile strength than the prior formulation. PERC was fortunate to find a comparable paper for use in PERC 2.

    Feminine hygiene products, in particular, are known to contribute to drainline blockage problems. These products exhibit a host of different properties. They employ proprietary and diverse materials, have differing and complex geometries, weights, densities and a host of other attributes that are unique to the specific brand and design. While it would have been desirable to incorporate feminine hygiene products into the PERC designed experiments, the cost of doing so would have been overwhelmingly prohibitive and the findings limited to the brands, models and loadings selected for the study. In essence, this product is highly variable and constantly evolving, making research using these materials extremely difficult and expensive.

    Finally, it needs to be recognized that flushing certain materials that are not intended or designed to be flushed into a building drain constitutes an abuse of the sanitary system. PERC recognizes this is a reality that the plumbing trade and facility owner encounter with regularity. However, attempting to determine an efficacy tipping point by including these materials into a research study sends a wrong message. The efficacy limits of our sanitary systems should not be determined by assigning an arbitrary level of abuse. Rather, we must hold the manufacturers of these materials accountable for how their products are used and call for a more coordinated educational program to inform consumers on the appropriate means of disposal for their products and the consequences of improper disposal.

  12. The study results show that while ‘chaotic’ activity in the drainline resulted from the testing at the 3.0 and 3.8 Lpf flush volume levels, the apparatus did not overflow at the flush station where toilets would normally be installed. Why can’t PERC therefore suggest that 3.0 or 3.8 Lpf is sufficient for the drainline transport of waste?

    The PERC Phase 1 and Phase 2 studies were conducted on a near perfect drainline. Because the test apparatus did not overflow during the testing should not be interpreted to indicate that overflows would not occur in a real building drain that is likely to include various snag points, such as horizontal junctions. Rather, PERC derives study recommendations based on the significant changes in the behavior of the test media as flow volumes are reduced.

  13. Based on the significance of toilet paper in the studies, will PERC recommend a minimum ‘specification’ for toilet paper?
    No. PERC has no interest in developing such a specification. Our characterization and recommendations regarding the impact of toilet paper on DLT are clearly stated in the report.
  14. Are any changes to the construction codes or product standards recommended as a result of this testing?
    One of the most significant findings in the PERC 2 study was that a reduction in pipe size diameter from 4” to 3” did not reliably improve drainline transport in long, commercial building drains.

    This should not be interpreted as a lacking result. To the contrary, the PERC research provided needed data and findings on the merits of pipe size reduction that had been debated in the industry for decades. This is a very useful and significant finding. Therefore, while a change to the codes regarding sanitary system pipe sizing requirements is not supported by the PERC findings, the significance of the findings remain profound.

    As this question pertains to product standards, PERC members will continue to participate at the various standards development venues to discuss the studies’ findings and to work collaboratively with the standards development committees to determine if revisions to the current requirements contained in the product standards are appropriate.