How Upflush Toilets Defy Gravity: The Simple Science of Maceration and Vertical Lift

If you’ve ever told someone you want to add a bathroom in your basement, you probably heard the same response: “You can’t. Water doesn’t flow uphill.”

It’s a fundamental rule of plumbing, drilled into us by gravity. To install a toilet, you need to be above the main sewer line, or you need to break open your concrete foundation to install a massive, expensive sump pit.

But what if I told you that’s not true?

There’s a technology that allows you to “cheat” gravity. It’s called an upflush system, and it’s not magic—it’s just incredibly clever engineering. Let’s break down exactly how this “impossible” toilet works, in three simple steps.

Think of the system as three parts:
1. The Toilet: It looks normal, but it flushes backwards into…
2. The Box: This is the brains and the muscle, sitting right behind the toilet.
3. The Skinny Pipe: This is the “escape route” that runs up your wall.

Here’s what happens in the 10 seconds after you flush.

Step 1: The Flush (Activation)

You press the flush handle.

Unlike your regular toilet, which uses an “S” shaped trap to send waste down into the floor, an upflush toilet sends everything out the back, directly into the sealed macerator box behind it.

Inside this box, there’s a smart switch. On many modern units, it’s a pressure sensor, part of the “auto-start/stop technology.” As the water and waste from the flush fill the box, the water level rises. This change in pressure triggers the switch, which instantly shouts, “Time to work!”

Step 2: The Blend (Maceration)

The moment that switch is triggered, the “muscle” of the system roars to life.

This is the macerator. It’s a powerful motor—sometimes 750W or more, like in many popular units—connected to a set of razor-sharp stainless steel blades.

Think of it as a heavy-duty kitchen blender.

For about 5 to 10 seconds, those blades spin at thousands of RPM, turning everything inside the box (waste and toilet paper) into a fine, watery liquid. We call this a slurry.

This step is the entire secret. Why? Because you can’t pump solids, but you can absolutely pump a liquid. The macerator’s job is to turn the “un-pumpable” into the “pumpable.”

Step 3: The Push (Pumping)

As soon as the blending is done, the second part of the system takes over: the pump.

This isn’t just any pump; it’s a high-pressure discharge pump. Now that it has a smooth slurry to work with, it can do something amazing. It injects this slurry into a very small discharge pipe, often only 1 inch or 1.5 inches wide.

Because the pipe is so narrow, the pump can create enormous pressure, allowing it to push that slurry up.

This is where you see those incredible numbers. A well-designed pump can push that slurry 20, 30, or even 36 feet straight up. That’s more than three stories high! It can also push it horizontally, sometimes over 300 feet, all the way across your house if needed.

This skinny pipe, which is easily hidden inside a standard 2x4 wall, runs up to your ceiling, across, and then connects to your home’s main sewer stack. Gravity takes over from there.

The whole process—flush, blend, push—is over in about 10-15 seconds. The box is empty, the pump’s sensor registers the pressure drop, and the system shuts off automatically. It’s now clean, empty, and waiting for the next flush.

So, when someone tells you water can’t flow uphill, you can tell them they’re right. But a “toilet slurry” in a 1-inch pipe with a 750W motor behind it? It can go wherever you tell it to.