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Choosing a Toilet: Flush Ratings, Heights, Shapes and Wall-Hung Options

By the JDI Construction teamReviewed by Arthur Kulchitskiy, Project Consultant, and Denise Lacquement, Designer (bathroom specialist)Updated October 20267 min read

Quick answer

Any toilet installed in Washington must flush 1.28 gallons or less and meet the WaterSense performance test, so every new model saves water. Choose on fit and comfort instead: measure your rough-in (finished wall to the center of the floor bolts), pick a bowl height that suits the people using it, choose elongated or round for the space, and decide on one-piece, two-piece or wall-hung before the walls are closed.

Every toilet you can legally install in Washington is a low-flow toilet, so the real choices are about fit, comfort and cleaning. The decisions that matter most are made early: the rough-in distance and the floor or wall structure decide which models will fit, and a wall-hung toilet has to be chosen before framing. This page covers the flush rules, how flush performance is tested, bowl height and shape, the main toilet types, and what to check before you buy.

Flush volume: what Washington allows

Washington's plumbing code sets the limit. Under the state's amendment to the Uniform Plumbing Code (WAC 51-56-0400, UPC 411.2), the effective flush volume of every toilet "shall not exceed 1.28 gallons (4.8 L) per flush", and the toilet must also meet the EPA WaterSense high-efficiency criteria. That is stricter than the federal limit of 1.6 gallons per flush in 10 CFR 430.32, which still appears on older toilets and in older advice.

Washington's appliance efficiency law separately limits what may be sold in the state for toilets manufactured on or after January 1, 2021. That law refers to California's standard rather than stating a number, so for the figure itself rely on the plumbing code above. A toilet bought online, from out of state or from a salvage yard should be checked before it is installed. The flush volume is printed on the china behind the seat or inside the tank.

Rule	Limit	Source
Washington plumbing code (what may be installed)	1.28 gallons per flush maximum, plus WaterSense performance	WAC 51-56-0400, UPC 411.2 and 411.2.2
EPA WaterSense label	1.28 gallons per flush or less	WaterSense Specification for Tank-Type Toilets, Version 1.2
Federal limit (for comparison)	1.6 gallons per flush for gravity tank toilets	10 CFR 430.32(q)

Dual-flush toilets offer a smaller flush for liquids and a full flush for solids. For WaterSense purposes their effective flush volume is the average of two reduced flushes and one full flush, which is how a dual-flush model with a full flush slightly above 1.28 gallons can still qualify. Our page on rebates, WaterSense and water savings covers what a lower flush means for your water bill and whether any local rebate applies.

Flush performance: WaterSense testing and MaP

A low flush volume is only useful if the toilet clears the bowl the first time. Two tests are worth understanding.

The WaterSense flush test. To earn the label, a toilet must "completely clear all test media from the fixture in a single flush in at least four of five attempts." The test load is 350 grams of soybean paste test media plus four balls of toilet paper. EPA reports that this test has since been adopted into the national ceramic fixture standard (ASME A112.19.2/CSA B45.1), so all tank-type toilets sold in the U.S. and Canada must now meet it, labeled or not.
MaP (Maximum Performance) testing. MaP is a separate, voluntary third-party test. EPA describes it as measuring "the maximum quantity of soybean paste test media (up to 1,000 grams) that toilets can clear." It is a way to compare models above the required minimum. WaterSense sets no MaP score, and no MaP figure is a code requirement.

Use a MaP result as one comparison among several, not as a pass mark. Bowl shape, trapway glazing, the size of the water surface in the bowl and how easily the toilet cleans all affect daily satisfaction as much as the test number.

One-piece, two-piece and wall-hung

Type	How it is built	Good for	Watch for	Relative cost
Two-piece	Separate tank bolted to the bowl	Most budgets and replacements; the widest choice of heights and rough-ins	The joint between tank and bowl collects grime and can leak at the bolts over time	Lower to mid
One-piece	Tank and bowl cast as one unit	Easier cleaning, a sleeker look	Heavier to carry and set; replacing a cracked tank means replacing the whole toilet	Mid to higher
Skirted (concealed trapway)	Smooth sides hide the S-shaped trapway	Easy wipe-down at floor level	Some models need a special mounting kit; check the rough-in range	Mid to higher
Wall-hung	Bowl mounts to the wall; tank and steel carrier sit inside the wall	Small rooms, cleaning the floor underneath, setting a custom seat height	Must be planned before framing; needs a deeper wall and an access panel at the flush plate	Higher to highest

What a wall-hung toilet involves

A wall-hung toilet is a framing and plumbing decision, not a fixture swap. The in-wall carrier is a steel frame that carries the bowl's load to the floor, with the tank inside the wall behind a removable flush plate. The drain usually leaves through the wall instead of the floor, so the waste line has to be rerouted. The carrier's spec sheet gives the wall depth it needs, which is often more than a standard interior partition. Choose the carrier and bowl together, since they are designed as a matched system, and keep the flush plate accessible for future service. Plan for this at the design stage, the same way you would for moving a toilet or other plumbing.

Bowl height and shape

Toilet heights are usually sold in two groups: a standard height and a taller "comfort" or "chair" height. Manufacturers measure differently (some to the rim, some to the top of the seat), so compare the seat height on the spec sheet, not the marketing name.

For reference, the 2010 ADA Standards, which govern public and commercial buildings rather than private homes, place the top of an accessible toilet seat 17 to 19 inches above the floor, and permit 15 to 19 inches in residential dwelling units they cover. Designers use those figures as a guide when planning for an older adult or someone with limited mobility. Our aging-in-place bathroom design page explains how toilet height fits with grab bars and turning space.

Elongated bowls are longer front to back. Many adults find them more comfortable, and they can be easier to keep clean around.
Round bowls project less into the room, which helps in a tight powder room or where the door swings near the toilet.
Compact elongated models give an elongated seat within a shorter overall length, a useful middle ground for small baths.

Washington's plumbing code sets minimum space around a toilet, including the distance from its center to a side wall and the clear space in front of it. Those clearances are covered with their sources on our bathroom plumbing code page. If a longer bowl would crowd the space in front, check the drawing before you order.

Rough-in: the measurement that decides what fits

The rough-in is the distance from the finished wall behind the toilet (not the baseboard) to the center of the closet bolts that hold the toilet to the floor flange. Toilets are made to fit specific rough-in distances, and the spec sheet for each model states the one it is designed for. A toilet ordered for the wrong rough-in either will not fit against the wall or will sit with an awkward gap behind the tank.

Measure with the old toilet in place, from the wall surface to the center of the bolt caps. If there are two pairs of bolts, use the rear pair.
If the remodel adds thicker wall tile or a new wall surface behind the toilet, the finished-wall position moves forward. Measure from where the finished wall will be.
Older houses sometimes have a rough-in that matches fewer models. Find out before you shop, not on installation day.
Changing the rough-in means moving the flange, which is plumbing work. In a full remodel with the floor open, this is the time to set it where you want it.

What to check before you buy

The flush volume is 1.28 gallons or less, printed on the fixture or the spec sheet, and the model carries the WaterSense label.
The rough-in on the spec sheet matches your measured distance from the finished wall.
The seat height on the spec sheet suits the people who will use it most. Sit on a display model if you can.
The overall length still leaves the code clearance in front of the bowl and clears the door swing.
For a wall-hung toilet: the carrier's required wall depth, its weight rating, and where the access panel will go.
For a skirted toilet: whether it needs a special mounting kit and whether that kit is included.
Whether a seat is included, and whether you want an outlet behind the toilet for a future bidet seat.

How JDI handles the toilet in a remodel

In our bathroom remodels we confirm the rough-in and the finished-floor height before the toilet is ordered, set a new flange where the floor is opened, and draw the clearances on the 3D design layout so you can see how the bowl sits against the vanity and door. Plumbing work is permitted and inspected. If you are planning a full room, our bathroom remodeling service in Vancouver page explains how a project runs, and a free in-home consultation is the place to measure yours.

Common questions

Can I still buy a 1.6 gallon toilet in Washington?

Not for installation under Washington's plumbing code. The code limits every toilet to an effective flush of 1.28 gallons and requires it to meet the WaterSense high-efficiency criteria. The 1.6 gallon figure is the older federal limit, which Washington's rules are stricter than.

Does a lower flush volume mean more clogs?

It should not with a current model. The flush test that WaterSense introduced, clearing 350 grams of test media in at least four of five flushes, is now part of the national standard for all tank toilets. Clogs in an older house are often a drain line problem rather than a toilet problem, so mention any history of backups to your plumber.

Is a taller toilet always better?

No. A taller bowl is easier for many adults to sit down on and stand up from, but children and shorter adults can find their feet do not rest flat on the floor. If one bathroom serves the whole family, sit on display models at both heights before choosing.

Can I move my toilet a few inches when I remodel?

Often, but it depends on what is under the floor. In a house over a crawlspace the drain can usually be rerouted; on a slab it means cutting concrete. Joist direction matters too. A move of any size involves the drain and vent and needs a plumbing permit.

Do I need to replace a toilet that still works during a remodel?

Not necessarily, but a remodel is the cheapest time to do it, because the floor is open and a new wax seal and flange are part of the work anyway. If you keep the old toilet, have the flange checked and set on the new finished floor height.

Sources

Checked October 2026. Rules, fees and programs change; confirm the current requirement with the agency before you rely on it.