Toilet Flush Tests: Beyond MaP, What Else Matters?

What MaP does and does not tell you

MaP (Maximum Performance) is a widely quoted number that appears in many toilet spec sheets. It reports the maximum grams of waste that a toilet can clear in a single flush under controlled laboratory conditions. A high MaP score, for example 1,000 grams, is often treated as proof that a toilet flushes powerfully.

But MaP is only one test. It does not tell you how well a toilet cleans its own bowl, how much waste sticks to the surface, or how well the toilet transports waste through a drainline. It also does not reflect differences in water pressure, pipe diameter, or the age and slope of the drain system in a real home. For a full picture of flush performance, you need to look beyond MaP to the official standards that regulators and independent certifiers use.

The ASME/CSA baseline: the standard behind the label

The most important official standard for toilet flush performance in North America is the combined ASME A112.19.2/CSA B45.1 standard, titled Ceramic Plumbing Fixtures. This standard defines both water efficiency and performance requirements for tank-type toilets, and it is referenced directly by the EPA's WaterSense program.

According to the EPA, WaterSense adopted its performance criteria from this standard and worked with stakeholders to develop the tests that are now part of it. In practice, all WaterSense labeled tank-type toilets must comply with, and be independently certified to meet, the same performance requirements as standard toilets. That means the performance tests are not optional marketing claims; they are verified by a third party.

The four performance pillars of the WaterSense specification

The EPA's Residential Toilets page lists four specific performance requirements that every WaterSense labeled tank-type toilet must meet. They are the closest thing to an official definition of real-world flush performance.

The first is mixed testing media flushability. This test uses a mixture of floating and sinking media of different sizes and densities to verify that the toilet can push both light and heavy material out of the bowl.

The second is bowl surface cleaning. This test checks the ability of the toilet to clean the surface of the bowl, which is what prevents streaks and stains from accumulating after repeated flushes.

The third is drainline waste transport. This test measures how far the toilet can move waste media through a horizontal drainline, which is a direct predictor of clogging in real pipes.

The fourth is waste extraction. This test uses soybean paste test media and toilet paper, meant to be representative of human waste, to verify that the toilet clears the bowl completely in a single flush.

What these tests mean for you as a buyer

When you compare toilets, you will rarely see the ASME/CSA numbers listed in a retail spec sheet. Instead, manufacturers and retailers usually quote the MaP score. That is fine as a starting point, but it is not the whole story.

If a toilet carries the WaterSense label (or is certified to the ASME A112.19.2/CSA B45.1 standard), you already know that it has passed all four performance tests described above. The label is a stronger guarantee of real-world performance than any single MaP number.

When you compare two WaterSense labeled models, you can look at the specific test results that the manufacturer publishes in its specification documentation. Some manufacturers list the waste extraction result, the bowl surface cleaning result, or the drainline transport distance. These numbers give you a more granular view than the MaP score alone.

If you are considering a toilet that is not WaterSense labeled, the MaP score is still useful, but you should be aware that the four performance dimensions are not covered. In that case, look for the ASME/CSA compliance mark or the manufacturer's published test reports.

Beyond the lab: paper, plumbing and habits

No laboratory test can fully replicate your home's plumbing. Your toilet's drainline size, the slope of the pipe, the venting, and the water pressure in your home all affect flush performance in ways that no test can fully anticipate. A toilet that performs well in a lab may still clog if your drainline is old, corroded, or poorly vented.

Even the type of toilet paper you use matters. Thick, plush paper that does not dissolve quickly can reduce the effective performance of even the best toilet. The waste extraction test uses a specific type of toilet paper, but your paper may behave differently.

Your flushing habits also play a role. Flushing twice is rarely necessary on a WaterSense labeled toilet, but if you are used to an older model that needed it, you may need a short adjustment period. Trust the test results and give the new toilet a few days to prove itself.

How to choose a toilet with confidence

Start by narrowing your search to models that meet the WaterSense specification or the ASME/CSA standard. That automatically filters out toilets that have not been independently verified. From there, use the MaP score as a secondary indicator, and read the manufacturer's published test report if one is available.

If you are choosing a 1.28 gpf model, the water-saving choice, you need the same performance verification as a 1.6 gpf toilet, and the WaterSense label confirms it. If you prefer a dual-flush toilet, make sure the reduced flush mode is part of the certified performance, not just the full flush mode.

For homes with older or longer drainlines, pay special attention to the drainline waste transport test. If the manufacturer does not publish that number, a 16-gram or higher MaP score is a reasonable proxy, but it is not the same as a documented transport distance.

Finally, remember that WaterSense certification is not a one-time design review; it is an independent, third-party certification. That means a certified toilet has been tested and verified, not just designed on paper. That is the strongest assurance you can get without testing the toilet in your own home.

What to pick for your use

Questions

Is MaP the same as the ASME/CSA test?

No. MaP is a separate, voluntary test that measures waste extraction only. ASME A112.19.2/CSA B45.1 is the national plumbing standard and includes waste extraction as one of several tests, along with mixed-media flushability, bowl surface cleaning, and drainline waste transport.

Does WaterSense require MaP testing?

No. WaterSense requires compliance with the ASME/CSA performance criteria, which include a soybean paste waste extraction test. MaP is an additional industry test that is not part of the WaterSense specification.

What is the soybean paste test?

The waste extraction test in the ASME/CSA standard uses soybean paste and toilet paper as a stand-in for human waste. It verifies that the toilet clears the bowl completely in a single flush.

If a toilet is not WaterSense labeled, can it still perform well?

Yes. Some manufacturers choose not to seek WaterSense certification even though their toilets pass the ASME/CSA tests. In that case, look for the ASME/CSA compliance mark or ask the manufacturer for the test report.

How much do drainline conditions affect flush performance?

Drainline conditions matter as much as the toilet itself. A toilet that passes the drainline waste transport test in a lab may still clog if your pipe is narrow, corroded, or improperly vented. If you have old plumbing, consider a model with a high transport distance result.

Does a higher MaP score mean a better toilet?

Not necessarily. A very high MaP score indicates strong waste extraction, but it does not measure bowl surface cleaning or drainline transport. A toilet with a moderate MaP score and excellent results in all four ASME/CSA categories is likely to perform better in daily use.