Short definition
A pressure-assist toilet uses a sealed inner tank that compresses air as supply water enters; on flush, the compressed air rapidly expels water through the bowl with much higher velocity than a standard gravity flush. Result: a powerful flush at 1.0 to 1.28 gpf, fewer clogs, no double-flushing — and a much louder “woosh” than a quiet gravity toilet. Sloan Flushmate is the dominant cartridge brand.
What it is
Inside the porcelain tank sits a separate plastic pressure vessel — the cartridge. As supply water flows in, the rising water level compresses air trapped above it. When you flush, a valve releases the pressurized water rapidly through the flush valve and into the bowl, scouring the bowl with high velocity.
Pressure-assist requires at least 25 psi static water pressure (per Sloan Flushmate spec). Households below that won’t pressurize the cartridge fully, and the flush goes weak.
The cartridge ages out at 10 to 15 years and is replaceable ($100 to $200 part). One historical note: Sloan Flushmate had a 2012 to 2013 recall on certain Series 503 cartridges (cracking risk). Series 504 and onward addressed it; homeowners with older Series 503 units can register on the Sloan Flushmate site for a free replacement.
Why it matters to a homeowner
Pressure-assist is the answer for high-traffic family bathrooms where 1.6 gpf gravity toilets double-flush constantly. The single-flush success rate is much higher at lower water volumes, so total water use drops below what the bowl is rated for in normal use.
The trade-offs: the flush is noticeably louder (an issue in a master bath next to a bedroom), the cartridges cost more than gravity-toilet parts, and minimum 25 psi static pressure is required. If your home has a low-pressure issue, fix that first or stick with a gravity HET.
When a contractor mentions “Flushmate,” “power-flush,” or “sealed-tank toilet,” that’s this category.
Common failure modes
- Cartridge ages out (10 to 15 years typical). Replace.
- Inlet supply line clogged with debris. Cartridge can’t fully pressurize.
- Series 503 recall (2012-2013 Flushmate). Register on Sloan Flushmate site for replacement.
- Loud operation. Acoustic issue, not a defect — choose accordingly.
Common variants
- Pressure-assist (sealed inner tank, compressed air) vs. gravity-flush (open tank, simple).
- Pressure-assist vs. dual-flush. Different efficiency strategies.
- Sloan Flushmate vs. proprietary cartridges from American Standard or Crane.