For a busy commercial restroom, a flushometer toilet is usually better: it flushes back to back with no tank to refill. But it needs a 1-inch supply and 35 to 45 psi of flow pressure. For a low-use restroom, or a building with small pipes or weak pressure, a tank toilet is often the better fit.
How do the two types work?
The EPA says commercial toilets, or flushometer-valve toilets, have "two main components," the toilet bowl and the flushometer valve. There's no tank. When someone flushes, the valve opens and sends a short, high-flow burst of water straight from the supply line into the bowl, then closes on its own. The IPC requires that "When operated, the valve shall automatically complete the cycle of operation, opening fully and closing positively under the water supply pressure."
A tank toilet stores water in a tank and releases it by gravity. After each flush, the IPC says the fill valve has to "refill the tank after each discharge and to shut off completely the water flow to the tank when the tank is filled to operational capacity." Until the tank refills, the next flush is weaker or doesn't happen.
There's also a middle option. A flushometer tank, often called pressure-assist, uses a sealed tank that stores water under pressure. The IPC lists it separately, with its own lower supply needs.
How do their supply and pressure needs compare?
This is the biggest difference. Here's what the IPC requires at each toilet's supply:
| Toilet type | Minimum supply pipe (Table 604.5) | Flow rate (Table 604.3) | Flow pressure (Table 604.3) |
|---|---|---|---|
| Flushometer valve, siphonic | 1 inch | 25 gpm | 35 psi |
| Flushometer valve, blowout | 1 inch | 25 gpm | 45 psi |
| Flushometer tank (pressure-assist) | 3/8 inch | 1.6 gpm | 20 psi |
| Tank, close coupled | 3/8 inch | 3 gpm | 20 psi |
| Tank, one piece | 1/2 inch | 6 gpm | 20 psi |
A flushometer valve pulls about 25 gallons per minute for a few seconds. Several flushing at once can drop pressure in a building with an undersized water service. The IPC also says flushometer valves "shall not be used where the water pressure is lower than the minimum required for normal operation." If the street pressure can't meet those numbers, the code calls for a booster: "a water pressure booster system conforming to Section 606.5 shall be installed on the building water supply system."
So before you choose, check the building. Ask for the size of the water meter and service line, and have a plumber measure the flowing pressure at the fixture while representative fixtures operate. Compare that available pressure and flow with the code table and the selected valve and bowl instructions. A static gauge reading alone does not establish whether the supply can support a flush. If a building runs close to the minimum, a restroom full of flush valves can leave the last toilet in the line with a weak flush. A converted retail space or an older building may have a water service sized for a couple of tank toilets, not a bank of flush valves. Our page on a water booster pump for low pressure explains that fix.
Which uses less water?
Both types are held to the same limit, and in Phoenix that limit is lower than the model code. The 2024 IPC's Table 604.4 allows 1.6 gallons per flushing cycle for a water closet. Phoenix's amendments replace it with Table 604.4(1), which caps a water closet at 1.28 gallons per flushing cycle and a urinal at 0.5. The old 1.6 limit survives only in Table 604.4(2), for listed exceptions such as a building "more than six (6) stories above grade plane," one "larger than 50,000 ft2" with a booster pump, or a care facility. Blowout water closets "having a water consumption not greater than 3 1/2 gallons" per flush are exempt from both tables. So for most new Phoenix restrooms, plan on a 1.28 gpf valve and bowl, not a 1.6. Our page on low-flow fixture requirements in Arizona covers the limits for homes.
For flushometer-valve toilets, the EPA says WaterSense labeled models "use no more than 1.28 gpf, which is a 20 percent savings over the federal standard of 1.6 gpf." There's a floor, too. EPA set "a minimum flush volume of 1.0 gpf to ensure plumbing systems have adequate flow to function effectively," after stakeholders worried that very low flushes "may result in blockages within commercial buildings with longer drainlines." Long horizontal drain runs are common in commercial buildings, so that minimum matters.
Older buildings are where the savings are. The EPA estimates that about "26 percent (7 million)" of installed flushometer-valve toilets use "3.0 to 7.0 gallons per flush." If your restroom still has old valves, replacing the valve and bowl together is often worth a look. Note that the valve and bowl have to match. A low-flow valve on an old high-flow bowl won't clear well.
How do they compare day to day?
Here's how they tend to stack up in a commercial setting.
Flushometer valve strengths
- No refill wait. Line pressure means the next user gets a full flush right away.
- Built for traffic. Valves are made for heavy, repeated use, and the internals can be rebuilt.
- Sensor and wall-hung options. Automatic sensor valves and wall-hung bowls are common, which helps with cleaning and hands-free use.
- Fewer tank parts. There's no tank lid, flapper or fill valve to be broken or tampered with.
Tank toilet strengths
- Smaller pipes and lower pressure. A 3/8-inch or 1/2-inch supply and 20 psi is enough.
- Quieter. A gravity flush is gentler, which suits small offices and single-user rooms.
- Familiar parts. Flappers and fill valves are easy to find.
Both have to meet the same commercial fixture rules. The IPC requires that "Water closet bowls for public or employee toilet facilities shall be of the elongated type," and that seats for those facilities "shall be of the hinged open-front type."
### What maintenance does each need?
A flushometer valve has a diaphragm or piston that wears and collects debris. Zurn's parts list, for example, includes a "Diaphragm Repair Kit" and a "Vacuum Breaker Repair Kit" for its valves. When a valve keeps running or short-flushes, a rebuild usually fixes it. Our guides to a flushometer that keeps running and urinal flush valve vacuum breakers cover the common repairs.
A tank toilet needs the usual flapper and fill valve care. Our page on replacing a toilet flush valve covers that.
Which should you choose?
Match the toilet to the room and the building.
- High traffic (restaurants, retail, gyms, event spaces, multi-stall restrooms): flushometer valves, if the water service and pressure support them.
- Low traffic (small offices, single-user or family restrooms): tank toilets are simpler and ask less of the pipes.
- In between, or weak pressure: a pressure-assist flushometer tank gives a stronger flush on a small supply.
If you're building out a new space, the choice also affects pipe sizing on the plans. Our guides to commercial tenant improvement plumbing, ADA commercial restroom plumbing and plumbing fixtures required for a restaurant, office or retail space cover the rest of the restroom plan.
HQ Plumbing & Air installs and services flushometer valves, commercial toilets and restroom supply lines across the Phoenix area, and we can check whether your building's pressure and pipe sizes will support flush valves. We're licensed and insured, available 24/7, and every job starts with a free estimate and upfront pricing. See our commercial plumbing services.
Busy restroom and strong supply: flush valve. Quiet restroom or small pipes: tank.