Toilet Rim Holes and Flush Power: More Holes vs Fewer

Every time you press the handle, water cascades from a ring of small openings drilled into the underside of the toilet rim. These are rim holes -- also called rim jets or rim ports -- and they are the hidden engineering variable that separates a sluggish 500-gram flush from one that clears a MaP-certified 1,000 grams of waste with a single pull.

Most homeowners never think about rim holes. Most plumbing guides skip them entirely. Yet toilet engineers at TOTO, Kohler, American Standard, and Gerber spend considerable R&D effort on jet geometry because it governs bowl rinse coverage, swirl momentum, clog resistance, and long-term cleanliness -- all without adding a single drop of extra water.

This guide explains exactly how rim holes work, what the research says about hole count versus hole size, why some high-performance toilets have eliminated the rim channel entirely, and how to read these specs when choosing a toilet for your home.

Toilet rim holes are small ports drilled into the inner ledge beneath the toilet rim through which tank water enters the bowl during a flush cycle. Water flows from the tank, through the rim channel (a hollow passage inside the porcelain rim), and exits through these jets at calculated angles to rinse the bowl walls and generate the rotational water column that forces waste through the trapway.

Recommended toilets in this guide

TOTO Aquia IV

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American Standard Champion 4

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American Standard Cadet 3

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Gerber Viper

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The rim channel acts as a manifold, distributing water from the tank inlet across the full circumference of the bowl. Each hole's diameter, angle relative to the bowl surface, and spacing determines how much of the bowl wall gets rinsed and with what velocity.

Standard toilets -- the kind found in most homes -- have between 6 and 30 rim holes depending on manufacturer design philosophy. Wide spacing between holes means each jet has more water pressure behind it but covers less surface area per hole. Close spacing means better coverage but each individual jet has less force.

The angle of the holes matters as much as the count. Holes angled tangentially (pointing sideways along the bowl wall) create a swirling motion that generates centrifugal force, helping water climb the bowl sides and then converge into the trapway. Holes angled more directly downward produce a curtain-wash effect, which is better for rinsing bowl walls but less effective at building swirl momentum.

When a rim hole becomes partially blocked -- by mineral deposits, hard water scale, or debris -- the flush pattern changes. You may notice one section of the bowl wall not getting wet during a flush. That asymmetry reduces swirl efficiency and can result in waste deposits accumulating in the unrinsed zone.

This is the core tension in rim hole design: coverage versus velocity.

High hole count (20 to 30+ holes) gives you a near-complete water curtain around the bowl interior. Every section of the bowl wall gets rinsed on each flush. This is excellent for hygiene -- bacteria and mineral deposits have fewer dry zones to colonize. It also prevents the brown or gray staining pattern you see in toilets where water never reaches certain sections of the rim curve.

Low hole count (6 to 12 holes) means each jet carries substantially more water per opening. The velocity at each point is higher, which generates more turbulence and swirl force. This can be advantageous for waste transport, particularly for solid waste that requires significant hydraulic momentum to move through the trapway.

The most honest answer is that hole count is a proxy for something more important: total swirl energy delivered to the water column at the start of the flush. A toilet with 10 precisely angled, correctly sized jets can outperform one with 28 smaller, randomly spaced holes on a MaP flush test while both use the same 1.28 gallons per flush.

Most toilets have both rim holes and a siphon jet. The two systems serve different phases of the flush cycle.

During the first fraction of a second after the flapper opens, water rushes from the tank into both the rim channel and the siphon jet. The siphon jet creates an immediate high-velocity stream aimed at the trapway entrance. This starts the siphon: it displaces water in the trapway, creates a pressure differential, and begins pulling the bowl contents through.

Simultaneously, rim jets flood the bowl walls with water. Their swirling action creates a rotating water column that concentrates bowl contents toward the center and then down into the trapway. The siphon action completes when air breaks the seal at the end of the flush.

In some older or very low-cost toilets, the siphon jet is absent or undersized. In those designs, rim jets alone must generate enough momentum to initiate siphon action -- which is why hole geometry is even more critical in washdown-style and rim-jet-only designs.

In TOTO's Tornado Flush system, the company essentially redesigned this whole architecture: rather than dozens of small rim holes, Tornado Flush uses two large nozzle ports positioned to create a powerful cyclonic swirl. The result is near-complete bowl coverage with fewer but larger jets and a more concentrated swirl pattern. This design achieves MaP scores of 1,000g while using only 1.28 GPF (Tornado Flush) or 1.0 GPF (in the TOTO Aquia IV dual-flush configuration on its 0.8 GPF full-flush setting paired with the larger flush).

This is one of the most underappreciated causes of declining flush performance in older toilets. The toilet that flushed perfectly when installed five years ago now leaves residue behind -- not because the toilet is worn out, but because its rim jets are progressively narrowing.

Hard water (defined as water with >120 mg/L of dissolved calcium carbonate) leaves scale deposits wherever water evaporates or sits. The rim channel is a perfect environment for this: water fills it during every flush, leaves behind minerals as it drains, and the dark, enclosed space allows buildup to accumulate undisturbed.

Signs of partially blocked rim holes include:

• Sections of the bowl wall that do not get wet during a flush
• Uneven or asymmetric water flow visible at the rim
• Persistent staining in areas below blocked jets
• Gradually worsening flush power despite no mechanical changes
• Hollow-sounding jets (some holes whistling, others silent)

Cleaning blocked rim holes typically involves pouring diluted muriatic acid or a commercial calcium/lime remover into the overflow tube inside the tank (which connects to the rim channel), letting it soak for 20 to 60 minutes, then flushing. For visible holes, a stiff wire or bent wire hanger can physically dislodge deposits after the chemical soak loosens them.

Toilets with fewer but larger rim holes -- like those using the Tornado Flush or Kohler's AquaPiston technology -- tend to resist mineral blockage better than designs with many small holes, simply because larger openings require more deposit accumulation to become functionally blocked.

Here is how the major brands approach rim hole design:

MaP scores sourced from published map-testing.com database. Scores listed are typical values for the standard configuration; exact scores vary by specific SKU and tank size. WaterSense certification requires 1.28 GPF or less.

Rimless toilet design -- common in European markets and increasingly available in the US through brands like Woodbridge and Swiss Madison -- solves a genuine hygiene problem. The hollow rim channel of a conventional toilet is essentially a closed tube that never dries out completely, creating ideal conditions for bacterial colonization and mold growth that standard cleaning cannot reach.

By eliminating the hidden rim channel, rimless designs expose all water-contacting surfaces to cleaning. This is a real advantage, and the European market has largely moved in this direction.

The engineering challenge is compensating for the loss of conventional rim-jet swirl. Rimless toilets use several approaches:

• Direct wash jets: Water enters from one or two points and is shaped to flow around the bowl in a controlled spiral using the bowl geometry itself
• Dual-direction jets: Some designs use two inlet points positioned to create counteracting currents that generate turbulence
• Reliance on siphon jet: More of the flushing work is assigned to the siphon jet rather than the rim

The tradeoff: rimless designs, while cleaner in hygiene terms, often have lower MaP scores than optimized conventional rim designs. Published MaP data shows most rimless toilets in the 500g to 800g range, while top conventional designs regularly hit 1,000g. For most households, 800g is more than adequate -- the vast majority of real-world waste events are below 600g. For households with chronic clogging issues or older pipes requiring maximum flush force, a conventional high-MaP design may serve better.

If hygiene and ease of cleaning is your priority, rimless is compelling. If you need maximum clog-clearing power -- perhaps for a toilet serving heavy use, children, or elderly household members -- the conventional optimized-jet designs still hold an advantage in raw flushing performance.

Blocked rim holes are among the easiest toilet maintenance tasks to handle without a plumber. The tools required cost under $10 and the process takes about 30 minutes of active work plus a chemical soak time.

Step 1: Confirm the Diagnosis

Hold a small mirror under the rim during a flush. Observe which holes are producing water flow and which are dry or producing only a trickle. Mark the blocked areas with a marker on the outside of the rim so you can reference them after the flush.

Step 2: Prepare the Cleaning Solution

For moderate calcium deposits, white vinegar is effective and safe for all porcelain and tank components. For heavy scale (toilets in very hard water regions, or fixtures that have not been cleaned in years), a commercial lime and calcium remover such as CLR or a diluted muriatic acid solution (1 part acid to 10 parts water) works faster. Always wear gloves and eye protection with acid-based cleaners.

Step 3: Deliver Solution to the Rim Channel

Turn off the toilet's water supply valve. Flush the toilet to empty the tank. The overflow tube in the tank connects directly to the rim channel. Pour your cleaning solution into the overflow tube using a small funnel. Use enough to fill the rim channel -- typically 8 to 16 ounces for a full-rim toilet. Plug the individual rim holes temporarily with plumber's putty or toilet paper to keep the solution in the channel rather than draining immediately.

Step 4: Soak and Clear

Allow the solution to soak for 20 to 60 minutes depending on severity. Then use a bent wire coat hanger, a straightened paper clip, or a commercial rim jet cleaning tool to physically probe each hole. The chemical soak softens deposits; mechanical action breaks them free. Work systematically around the rim.

Step 5: Flush and Verify

Remove any putty or paper plugs. Restore the water supply. Flush several times to clear the cleaning solution and loosened deposits from the rim channel. Return with the mirror and verify that all holes now produce visible water flow.

For prevention, adding a small amount of white vinegar to the tank monthly (pour it directly into the tank, not the bowl) can slow mineral accumulation in the rim channel without affecting the toilet's mechanical components.

When selecting a new toilet, consider that models with fewer but larger rim holes or nozzle-based flush systems (like TOTO Tornado Flush) require less maintenance to maintain full flush performance in hard water areas.

For a broader view of what makes a toilet perform reliably year after year, see our guide to best flushing toilets where we evaluate top models across all these dimensions.

Related reading: our MaP flush test explained guide covers how performance is measured and what scores to look for. For a technical breakdown of the flush mechanism, see how a toilet flush works. If you are dealing with chronic partial clogs, toilet clog causes and prevention addresses the full picture including trapway diameter, which works together with rim hole performance.

A common misconception is that upgrading to a toilet with a 3-inch or 4-inch flush valve (versus the standard 2-inch) is the single key to better flushing. Flush valve size does matter -- a larger valve opens faster and delivers a more concentrated surge of water at flush initiation, which improves siphon initiation speed. But that advantage is wasted if the rim channel cannot distribute the water effectively.

The American Standard Champion 4 -- whose name refers to its 4-inch flush valve and 2-3/8-inch trapway -- is a good example of a toilet that optimizes both elements. The large valve delivers high-volume water rapidly; the PowerWash Rim distributes it across the full bowl circumference; and the large trapway reduces the resistance waste encounters during transport. The result is a consistent 1,000g MaP Premium score.

Conversely, TOTO's Tornado Flush system achieves the same 1,000g MaP score with a standard flush valve size, because the two large nozzle ports and cyclonic swirl geometry extract more flush energy from the same water volume. The engineering approach is different but the outcome is equivalent.

For consumers evaluating toilets, the most reliable predictor of real-world flush performance remains the published MaP score -- not the valve size, not the hole count, and not the marketing terminology. A toilet with a 1,000g MaP Premium score will outperform one rated 600g regardless of which component the manufacturer chose to optimize.

To make this practical, here is a direct comparison of three dominant flushing architectures and what published data shows about their performance and maintenance characteristics:

No single architecture is superior across every dimension. The right choice depends on whether flush power, hygiene, or maintenance simplicity is your primary priority.

• EPA WaterSense, epa.gov/watersense
• MaP flush testing, map-testing.com
• Manufacturer published specifications
• TOTO USA engineering documentation on Tornado Flush technology
• American Standard published Champion 4 and Cadet 3 product data
• Kohler product specifications for Highline and Cimarron with AquaPiston
• Gerber Plumbing published Viper flushing system data

• Best Flushing Toilets: Top Picks for Every Bathroom
• What Is a MaP Flush Test Score and Why Does It Matter?
• How a Toilet Flush Works: Siphon, Flapper, and Flow Explained
• Why Toilets Clog: Causes, Prevention, and the Right Hardware
• GPF Guide: 1.28 vs 1.6 vs Dual Flush Water Efficiency