Sewage pump vs. grinder pump: which do you need?

Anytime you’re installing a pump in a bathroom below the sewer lines, gravity alone can’t move the wastewater—so you’ll need to choose between a sewage or grinder pump.

If you're working on a replacement sewage pump, it can seem as simple as looking at the model number and ordering a new pump, but what if installing the wrong one the first time led to the problems? And if you’re plumbing new construction, making the right choice means the homeowner will be satisfied with your work for years to come.

While the terms are sometimes used interchangeably, understanding the difference between sewage and grinder pumps is important to get the job done right the first time. Whether you’re replacing or installing new, discover how to choose the best residential sewage or grinder pump for the job.

What’s a sewage pump?

Unlike effluent or sump pumps, which should be used only to remove clear or gray water, sewage pumps are designed to move “dirty” or sewage waste to a septic tank, gravity flow sewer main or leach field. Also called sewage ejector pumps, some can move up to 200 gallons a minute of waste horizontally as far as 750 feet.

A sewage pump uses an impeller to provide the head pressure that moves the waste vertically. There are three general types of impellers: vortex, semi-open and enclosed channel. Each type of impeller and its dimensions correspond with different head pressures. A typical sewage pump will use a vortex-style impeller to prevent clogging and efficiently move the liquid.

Sump and sewage pumps usually have lower horsepower (hp) than grinder pumps. A sewage ejector pump with 1/2 hp is all that’s typically needed for a residential home. And because what goes in the septic pump must fit through the pipes “as is,” sewage pumps have larger diameters for discharge line and pump connection: between 1.5” to 3”.

Nine times out of 10, a regular sewage pump that doesn’t grind is what you’ll need for a residential plumbing job. But what about that other 10% of the time?

What’s a grinder pump?

Grinder pumps are a type of sewage pump, which can explain why people sometimes use both terms interchangeably. Residential sewage grinder pumps handle a lower volume of waste—between 35 and 70 gallons per minute—but over much longer distances, into the several thousands of feet.

In addition to having an impeller, grinder pumps use cutter blades to pulverize, or grind, solids. The slurry can then more easily pass through lines with smaller diameters than solid waste could, so the discharge line and pump connection is usually 2” or less, and some use 1.25”.

Grinder pumps are more powerful, starting at 1 hp. In general, they cost a bit more than regular sewage pumps and sometimes use more electricity. However, just as with normal sewage pumps, they can last for years if well maintained.

When to use a grinder pump vs. ejector pump

So if a grinder pump has more torque and chops up everything that comes its way, using one for every job seems like an easy decision to make.

But there are a number of reasons to stick to a sewage pump when the job calls for it, and not just because of the potentially higher energy costs of grinder pumps. Unfortunately, it’s a myth that grinder pumps can’t clog. Stringy materials can clog the pump and reduce efficiency over time.

And if you’re connecting to a septic tank, it’s not recommended to use a grinder pump at all. They pulverize the particles so well that solids can’t separate from the liquid, which is how septic systems work to treat wastewater.

If you need to pump to higher elevations and longer distances, particularly with smaller-diameter pipe, then a grinder pump is the right choice for the job. Because they typically handle lower volume, it’s best to use grinder pumps when flowing to a pressurized sewer main.

For moving high volumes of raw sewages short distances or to a septic tank, a sewage pump is the best choice and sometimes brings lower power usage along with it.

Ferguson can help you decide between a sewage and grinder pump

Whether you’re looking for a model number to replace a part or planning a new construction, our knowledgeable associates can help you select the specifications and features you need. Contact your local Ferguson to discuss which septic pump you need to get the job done right.