Best Mission Toilets (2026)
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Problem solving, plain language
Toilet Won't Flush Poop All the Way: Why and How to Fix
Solid waste left in the bowl after a flush points to one or more specific, fixable causes. This guide walks through every root cause, tested remedies, and the point at which a failing toilet warrants replacement rather than another repair.
Why Trust Best Flushing Toilets
- Flushing power and MaP flush-test scores
- Water efficiency (GPF and EPA WaterSense)
- Aggregated owner reviews
- Clog resistance and trapway design
- Brand reliability and warranty
Research updated June 2026.
Quick Answer
A toilet that leaves solid waste behind almost always has one of four culprits: low tank water level, a worn flapper releasing water too slowly, a partial trapway blockage, or a flush system that simply lacks the power for the load. Most cases resolve with a water-level adjustment or flapper swap without calling a plumber.
A flush that doesn't clear poop is one of the most embarrassing and frustrating plumbing problems a household deals with. It happens more often than manufacturers like to admit, and it rarely means your toilet is broken beyond repair. In most cases the fix is mechanical, inexpensive, and takes under thirty minutes with basic tools.
Understanding why it happens requires a brief tour of how a gravity-flush toilet clears waste. When you press the handle, the flapper or flush valve opens and releases stored water from the tank into the bowl. That rapid inrush creates a siphon inside the S-shaped trapway, which is the curved passage connecting the bowl to the drain stack. The siphon pulls waste through the trap and into the sewer line. If the water volume is too low, the release too slow, or the trapway partially obstructed, the siphon breaks before waste exits, and solid material stays in the bowl.
The best flushing toilets are engineered to clear 800 to 1,000 grams of solid waste per flush according to Maximum Performance (MaP) testing, a North American standard operated independently of manufacturers. A toilet rated at 350 grams will routinely leave waste behind when faced with a normal load. Knowing your toilet's MaP score is the single most important diagnostic starting point.
What Is the Most Common Reason a Toilet Won't Flush Poop?
The most common reason is insufficient water in the tank. Most toilets need the tank to fill within one inch of the overflow tube for the flush to generate enough siphon force. If the float is set too low or the fill valve is worn, the tank never reaches that level, and the flush delivers too little water to fully pull solid waste through the trapway.
The second most common cause is a worn flapper that releases water gradually rather than all at once. A healthy flush needs water to enter the bowl fast. A slow-releasing flapper reduces flow rate, weakens the siphon, and leaves waste behind even when the tank holds the right volume.
To check tank water level, remove the tank lid and look for the fill line, usually a molded mark inside the tank or a sticker. The water surface should sit about half an inch below the top of the overflow tube. If it is lower, locate the fill valve float and raise it. On a ball-float design, bend the float arm slightly upward. On a cup-float or tower-float design, turn the adjustment screw clockwise or squeeze the clip and slide the float upward.
If adjusting the float produces no change in flush power within a week of normal use, the fill valve itself may be worn and delivering water too slowly even when the float is correctly positioned. Fill valve replacement is a straightforward repair: shut the water supply, flush to empty the tank, unscrew the locknut underneath the tank, lift the old valve out, drop in a new universal valve such as a Fluidmaster 400A, and reconnect the supply line. The entire job takes fifteen to twenty minutes.
Expert Take
Plumbing contractors consistently point to the fill valve as the most underrated cause of weak flushing. A valve that filled the tank to the correct level five years ago may now stop two inches short as the float or seal wears, silently robbing every flush of the water it needs. If a tank-level adjustment does not solve the problem, replace the valve rather than keep chasing other causes.
Can a Partial Clog Cause a Toilet to Not Flush Poop?
Yes. A partial blockage in the trapway or drain stack is a very common cause of this symptom. Unlike a full clog that causes overflow, a partial clog narrows the passage so waste cannot exit cleanly but water can still drain slowly. The toilet appears functional until it is asked to move solid material.
Signs of a partial clog include slow draining after a flush, water rising higher than normal before draining, occasional gurgling from the toilet or nearby fixtures, and a pattern where poop remains but liquid waste flushes normally. A toilet auger or closet snake resolves the majority of partial trapway clogs without chemicals.
To address a partial clog, start with a proper plunger technique. A flange plunger, which has an extended rubber skirt that fits inside the drain opening, creates far more suction than a cup plunger. Insert the flange into the drain opening, press down to form a seal, and pump vigorously eight to ten times before pulling up sharply to break the seal. Repeat three to five cycles. If the drain speeds up noticeably after plunging, you had a partial soft clog that has now cleared.
For clogs that resist plunging, a toilet auger (also called a closet auger) is the next step. Feed the cable into the drain opening, crank the handle clockwise, and advance the cable until you feel resistance. Work the cable back and forth to break up or hook the obstruction. Pull the cable out, which often brings the clog material with it. Flush immediately to verify the blockage is cleared. See our detailed guide to snaking a toilet for a step-by-step walkthrough.
If the toilet continues to drain slowly after both plunging and augering, the obstruction may be deeper in the drain stack or a vent pipe may be blocked. A blocked vent prevents air from entering the system, which breaks the siphon effect prematurely. Vent issues typically affect multiple fixtures simultaneously. If your bathtub, sink, or other toilet also drain slowly, vent blockage is likely and the job requires a plumber with a drain camera.
Expert Take
Partial clogs caused by non-flushable wipes are among the most persistent plumbing complaints seen in surveys of professional plumbers. Even products labeled "flushable" often fail to break down quickly enough and accumulate in the trapway over time. Switching to standard toilet paper and stopping all wipe flushing resolves recurring partial clogs in the majority of households within two to four weeks.
Why Does My Toilet Flush Liquid Waste But Not Solid Waste?
This is a precise diagnostic clue. When a toilet handles liquid but leaves solid waste behind, it means the flush is generating some siphon force but not enough to clear denser material. The most likely causes in this scenario are a flapper opening only partially due to a chain that is too short or kinked, a water level that is borderline rather than critically low, or a toilet with a weak factory flush system.
It can also indicate a low-grade trapway obstruction that narrows the passage just enough to block solid material. Check the flapper chain slack, verify the water level, and try plunging even if the toilet does not appear fully clogged, since a partial restriction near the top of the trap is easy to miss.
The flapper chain is a small but surprisingly influential component. If the chain has too little slack, the flapper cannot seal fully and the tank constantly trickles into the bowl, so the tank never fills completely. If the chain is too long or kinked, it can prevent the flapper from opening fully, limiting how fast water enters the bowl. Ideal slack is approximately half an inch. Disconnect the chain from the handle arm and reconnect it to a link that gives that half-inch of looseness when the flapper is seated.
Flappers wear out over three to five years on average. A worn flapper seal releases water gradually over several seconds rather than all at once. Check by lifting the flapper while the tank is full and listening. If the tank starts to empty even before you press the handle, the flapper is leaking. If the flapper feels soft, deformed, or leaves a black residue on your fingers, replace it. Universal flappers from Korky and Fluidmaster are widely available, but for best results match the brand and flush valve diameter. TOTO uses a 3-inch flush valve on many models including the Drake; most Kohler toilets use 2-inch or 3-inch flappers depending on the generation.
| Symptom | Most Likely Cause | DIY Fix | Difficulty |
|---|---|---|---|
| Poop stays, water drains slowly | Partial clog in trapway | Plunge, then auger | Easy |
| Poop stays, drain speed normal | Low tank water level or weak flapper | Adjust float / replace flapper | Easy |
| Only liquid flushes cleanly | Flapper chain restriction or partial clog | Relink chain, plunge | Easy |
| Problem worsens over time | Fill valve wear or mineral buildup | Replace fill valve, descale jets | Moderate |
| Multiple fixtures slow | Vent blockage or main drain issue | Call a plumber | Professional |
| Every flush requires a second flush | Toilet's MaP score too low for household use | Toilet replacement | Moderate |
How Do Clogged Rim Jets Cause Incomplete Flushing?
Rim jets are small angled holes under the bowl rim that direct water into the bowl during a flush to help rinse the sides and amplify the siphon. In areas with hard water, mineral deposits accumulate inside these jets over months and years, gradually narrowing or fully blocking them. When enough jets are blocked, water enters the bowl too slowly and the siphon never fully activates, leaving waste behind.
You can inspect rim jets by holding a small mirror under the rim or shining a flashlight upward into the holes. Blocked jets appear white or tan from calcium buildup rather than dark and open. Cleaning them with a vinegar soak and a small wire or toothpick typically restores normal flow within one treatment.
To clean rim jets, pour one to two cups of white vinegar into the overflow tube inside the tank. The overflow tube connects directly to the rim jets in most gravity toilets, so this routes the vinegar to where it needs to go. Wait at least thirty minutes, then use a piece of wire or a stiff-bristled toothbrush to ream out each jet opening. For heavy deposits, repeat the vinegar treatment overnight by sealing the overflow tube with tape after pouring in the vinegar so it sits in the rim channel longer. See our article on cleaning under the toilet rim for a full walkthrough of this method.
In very hard water areas, this cleaning may be needed two to three times per year to maintain proper flush performance. If your water supply delivers more than 7 grains per gallon of hardness, consider a toilet from TOTO that uses the CeFiONtect ceramic glaze, which resists mineral adhesion more effectively than standard porcelain. The TOTO Aquia IV and TOTO Drake II both offer this glaze as a standard feature on most finishes.
When Should I Replace the Toilet Instead of Repairing It?
Replacement makes more economic sense than ongoing repairs when the toilet requires a second flush more than a few times per week, when it has a MaP score below 500 grams and the household load routinely exceeds that, when the porcelain is cracked, or when the cost of repairs begins approaching half the cost of a new unit. Toilets manufactured before 1994 may use 3.5 gallons per flush or more and will never match the clearing power of a modern 1.28 GPF design even after every repair is made.
A toilet with a MaP score at or above 800 grams that is properly maintained should serve most households without leaving solid waste behind. If yours reaches that threshold with all components in good condition and still fails, the bowl geometry or trapway design is the limiting factor, and replacement is the appropriate solution.
When evaluating replacement options, MaP scores are the single most objective measure of solid-waste clearing ability. The MaP testing program tests toilets by flushing progressively heavier loads of soybean paste in a sealed polyethylene bag, increasing the load in 50-gram increments until the toilet fails to clear the bowl in one flush. Published results are available at map-testing.com and cover thousands of toilet models.
Toilets that consistently earn the top 1,000-gram MaP score while using only 1.28 GPF include the TOTO Drake, TOTO UltraMax II, American Standard Champion 4 (at 1.6 GPF), American Standard Cadet 3, and Gerber Viper. If your current toilet has a MaP score you cannot find or a score below 400 grams, upgrading to any of these models will almost certainly eliminate the problem entirely.
The American Standard Champion 4 uses a 4-inch flush valve, the largest of any major residential toilet, which accelerates water release dramatically. Combined with a fully glazed 2 and 3/8-inch trapway, it achieves its 1,000-gram score at 1.6 GPF rather than 1.28 GPF, using slightly more water but providing an additional margin for households that experience frequent clogging with other models. For a broader look at options, the best toilets for flushing solid waste guide compares top-rated models specifically on this dimension.
Expert Take
Plumbers and licensed contractors who work on residential toilets daily report that the single biggest mistake homeowners make is spending money on repeated repairs to a toilet that fundamentally lacks the flush power for their household's needs. If a toilet was built before 2010 and has no visible MaP certification, the most cost-effective long-term solution is usually replacement with a high-MaP 1.28 GPF model that also qualifies for EPA WaterSense certification, since the water savings offset a portion of the purchase cost over time.
What Maintenance Prevents a Toilet from Leaving Poop Behind?
Three maintenance steps prevent the majority of incomplete-flush problems. First, inspect and replace the flapper every three to five years before it degrades enough to slow water release. Second, clean rim jets annually with a vinegar treatment if you have hard water. Third, check the tank water level seasonally and readjust the float if it has drifted below the fill line marked inside the tank.
Beyond these, using only standard toilet paper, keeping the trapway clear of foreign objects, and replacing the fill valve every seven to ten years as a scheduled maintenance item rather than waiting for obvious failure will keep a quality toilet clearing its full MaP-rated load throughout its service life.
A step-by-step maintenance schedule for most households looks like this. Monthly: flush and observe. Water should reach the bowl rim quickly, drain within fifteen seconds, and leave the bowl visibly clean with no skid marks on a bowl with standard glaze. If any of these benchmarks slip, investigate rather than wait. Annual: drop the tank lid and inspect the flapper seal, chain slack, and water level. Clean rim jets. Check the fill valve for the correct shut-off height. Every three to five years: replace the flapper proactively. Every seven to ten years: replace the fill valve even if it appears functional, since internal seals degrade invisibly.
One often-overlooked factor is what goes into the bowl. Excessive toilet paper in one pass, paper towels, baby wipes, and "flushable" wipes all increase the load on the flush mechanism. Even a toilet with a 1,000-gram MaP score is tested with a single discrete load in a sealed bag, not multiple sheets of thick paper added simultaneously. Reducing the volume of paper flushed per trip eliminates incomplete flushes for some households without any hardware change at all.
For households that cannot reduce paper use or where dietary factors produce consistently heavy loads, the toilets with the widest glazed trapways perform best. The American Standard Champion 4's 2 and 3/8-inch glazed trapway and the TOTO Drake's 2 and 1/8-inch glazed trapway both allow dense material to pass without snagging on unglazed ceramic. Narrow, unglazed trapways found in older or budget-tier toilets accumulate waste on rough surfaces over time and are a structural reason why some toilets become progressively worse flushers as they age. Read more on this topic in our trapway size guide.
Frequently Asked Questions
Why does my toilet not flush poop but flushes fine otherwise?
Liquid waste requires less siphon force to clear than solid material. When a toilet handles liquid but leaves solid waste, the flush is borderline, usually because the water level in the tank is slightly low, the flapper opens partially due to a short chain, or there is a minor trapway obstruction. Check the chain slack first, then the tank water level.
Can I use chemical drain cleaner to clear poop left in the toilet?
Chemical drain cleaners such as Drano are not recommended for toilets. They are not formulated for porcelain or the organic matter found in waste, they can damage the rubber flapper and seals inside the toilet, and they do nothing to address the underlying mechanical cause of incomplete flushing. A plunger and, if needed, a toilet auger are the correct tools.
How much water should be in my toilet tank?
The water surface inside the tank should sit approximately half an inch below the top of the overflow tube. Most manufacturers also mark a fill line inside the tank. If the water is more than an inch below the overflow tube, the flush is losing power, and the float should be raised to restore the correct level.
What MaP score do I need to avoid leaving poop behind?
MaP testing shows that a score of 600 grams covers a typical single adult load, but households with heavier use benefit from 800 grams or higher. Most plumbing professionals and consumer guides recommend choosing a toilet with a 1,000-gram MaP score for daily reliability across varying loads. Scores are published for free at map-testing.com.
Does a 1.28 GPF toilet flush as well as an older 1.6 GPF toilet?
Modern 1.28 GPF toilets with high MaP scores outperform most older 1.6 GPF models in flush performance. The improvement comes from better bowl geometry, larger flush valve openings, and optimized trapway dimensions that let the same volume of water move faster and generate a stronger siphon. The American Standard Cadet 3, for example, achieves a 1,000-gram MaP score at 1.28 GPF.
Why does my toilet sometimes need two flushes to clear poop?
A toilet that consistently requires a second flush is operating at or below its clearing capacity. The most common causes are a water level that is slightly low, a flapper that is beginning to degrade, or a toilet whose published MaP score is close to the typical household load. If adjusting the water level and replacing the flapper does not resolve it, the toilet may need replacement with a higher-MaP model.
Can a blocked toilet vent cause poop not to flush?
A blocked vent can definitely contribute. Vent pipes allow air into the drain system to maintain the siphon. When a vent is blocked by leaves, bird nests, or ice in cold climates, the air deficit weakens the siphon and may leave waste behind. The key indicator is that multiple plumbing fixtures in the home drain slowly at the same time. Vent clearing typically requires a plumber or a long drain snake fed through the roof vent opening.
How do I know if my flapper is the problem?
Add a few drops of food coloring to the tank without flushing, then wait fifteen minutes. If color appears in the bowl without a flush, the flapper is leaking and the tank is never reaching its full water level. Alternatively, press down on the flapper firmly while flushing; if the flush power improves noticeably, the flapper is not sealing or opening fully and should be replaced.
Do TOTO toilets flush better than American Standard for solid waste?
Both brands produce models that achieve the top 1,000-gram MaP score. The TOTO Drake and Drake II use a G-Max siphon-jet system that owners frequently praise for clearing heavy loads with a single flush. The American Standard Champion 4 uses a 4-inch flush valve that moves water extremely fast. Either brand at 1,000 grams MaP will resolve an incomplete-flushing problem caused by a weak toilet rather than a mechanical issue.
Can low water pressure cause a toilet to not flush poop?
Gravity-flush toilets do not rely on supply line water pressure to flush. The flush is powered entirely by the water stored in the tank dropping under gravity. Low supply pressure affects how quickly the tank refills after a flush but does not affect flush force. If the tank is full to the correct level, low street pressure is not the cause of an incomplete flush.
Should I use a pressure-assist toilet to solve this problem?
Pressure-assist toilets store compressed air in a sealed vessel inside the tank and use that air pressure to blast water into the bowl at higher velocity than gravity allows. They are very effective at clearing heavy loads and are rarely plagued by incomplete flushing. The trade-off is that they are louder than gravity models, more expensive, and require a minimum water pressure of 25 PSI at the supply line. They are a valid upgrade option for households that have exhausted mechanical fixes.
Is it safe to plunge a toilet if poop is still in the bowl?
Yes. Plunging is appropriate and effective when solid waste is still present. Use a flange plunger and work with slow, steady pressure rather than aggressive rapid strokes, which can splash. The waste will either break up and drain or be pulled back into the bowl and then drained with a strong flush once the obstruction clears. Wear gloves and have the floor covered if the bowl is near-full before you start.
Why does a new toilet sometimes fail to flush poop?
A new toilet may be installed with the water level set too low from the factory float setting, which is often conservative to reduce shipping splashing. Check the fill line inside the tank and raise the float if the water surface is more than half an inch below the overflow tube. If the toilet's MaP score is below 600 grams, that is a design limitation rather than an installation issue and may require a different model selection.
How long does a toilet flapper last?
Most rubber flappers last three to five years under normal use. Chlorinated water supplies, toilet-tank cleaning tablets, and bleach used inside the tank accelerate rubber degradation significantly, sometimes reducing lifespan to one to two years. If you use in-tank cleaning products, expect to replace the flapper more frequently and use a chlorine-resistant flapper designed for that environment.
Can a Kohler Highline or Cimarron handle heavy solid waste loads?
Both models achieve a 1,000-gram MaP score at 1.28 GPF and are among the most popular choices recommended for households that need reliable flushing of heavy loads. The Kohler Highline Arc and Kohler Cimarron use the Class Five flushing system, which delivers a large volume of water rapidly through an optimized bowl to create a strong siphon. Owner reviews consistently describe both as rarely clogging.
What is the Woodbridge T-0001 MaP score, and is it good for this problem?
The Woodbridge T-0001 is typically rated at 800 grams on the MaP scale at 1.28 GPF, which is sufficient for most households. It uses a dual-flush button system with a full-flush option for solid waste. While not at the very top of the 1,000-gram tier, most owner reports describe it as flushing solid waste reliably, and its skirted design with a fully glazed trapway reduces the buildup that degrades performance over time.
Does toilet bowl coating affect whether poop sticks or rinses away?
Yes, noticeably. TOTO's CeFiONtect glaze creates an ion-barrier surface that reduces the surface energy of the porcelain, making it much harder for waste, bacteria, and mineral deposits to adhere. Owners of TOTO toilets with CeFiONtect consistently report cleaner bowls between scrubbing and fewer skid marks compared to standard porcelain. American Standard's EverClean antimicrobial surface has similar benefits. Both coatings reduce the conditions that allow partial waste to stick to the bowl rather than drain fully.
How do I increase flush power without replacing the toilet?
Raise the tank water level to within half an inch of the overflow tube, replace the flapper if it is more than three to four years old, clean all rim jets with a vinegar treatment, and check that the flapper chain has the correct half-inch of slack. These four steps collectively maximize the flush power available from any existing toilet without spending money on a replacement. See our full article on how to improve toilet flush power for additional adjustments.
Sources
- EPA WaterSense, epa.gov/watersense
- MaP flush testing, map-testing.com
- Manufacturer published specifications
Our Verdict
A toilet that leaves solid waste behind is almost always fixable with a water-level adjustment, flapper replacement, or plunging. If those fixes fail, the toilet itself likely has a MaP score that cannot meet the household's daily demand, and upgrading to a 1,000-gram-rated model such as the TOTO Drake, Kohler Highline, or American Standard Champion 4 is the most reliable long-term solution.
Related Guides
How we rank & our data sources
We do not run physical lab tests. Rankings are built from published, verifiable data and real owner feedback, never paid placement.
- MaP (Maximum Performance) flush scores
- EPA WaterSense certification & GPF ratings
- Manufacturer specifications (trapway size, flush-valve, rough-in)
- Verified owner reviews from Amazon, Home Depot & Lowe’s
Researched by Derek Whitman · Last updated July 1, 2026 · Our review method
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