How Sewage Ejector Pumps Work

Sewage ejector pumps, also known as sewage lift pumps, are an essential component of many residential and commercial plumbing systems. They are used when gravity drainage alone is insufficient to remove wastewater from a building. In this comprehensive guide, we’ll explain what sewage ejector pumps are, how they work, their components, types, sizing calculations, installation, maintenance and troubleshooting.

What is a Sewage Ejector Pump?

A sewage ejector pump is a pump used to ‘lift’ wastewater from lower elevation fixtures and pump it to a higher elevation where it can then continue flowing by gravity again. Sewage ejector pumps are installed where the main sewer line leaving the property is too high for standard gravity drainage from the lowest plumbing fixtures.

Instead of connecting low elevation fixtures directly to the main sewer line, the fixtures drain into a holding tank called a sump pit. When the sump pit fills to a certain level, float switches activate the sewage ejector pump to pump the accumulated wastewater up to the elevation of the main sewer line where it can drain away normally.

Why are Sewage Ejector Pumps Used?

There are two main situations where sewage ejector pumps are required:

1. Basements and Low Levels Below the Sewer Line

In homes with basements or below grade rooms, it is common for showers, sinks, laundry and other fixtures on those lower levels to be below the elevation of the main sewer line. Gravity drainage relies on a continuous downward slope to drain, so wastewater from basement plumbing cannot flow ‘uphill’ to the main sewer line. An ejector pump lifts the waste up to the sewer line so it can drain.

2. Long Horizontal Drainage Runs

Even if a fixture is not located below the sewer line, a long horizontal distance to reach the sewer pipe can prevent proper drainage. Drainage lines should be sloped at least 1/4 inch per foot to maintain flow. If a fixture is too far away horizontally from the sewer connection, the necessary slope cannot be maintained and wastewater will not drain correctly. A sewage ejector pump is used to push the wastewater through a horizontal pipe run to reach the sewer line.

How Do Sewage Ejector Pumps Work?

Sewage ejector pumps work on the principle of a sump pump system. Here are the basic steps in their operation:

1. Wastewater Drains into Sump Pit

Fixtures draining to the ejector pump drain into a collection tank called a sump pit or sump basin. The pit contains a strainer to catch large debris before it reaches the pump.

2. Float Switch Activates at Preset Height

Inside the sump pit are float switches set at different heights. As the pit fills with wastewater, the floats rise with the water level. When the wastewater reaches a preset level, the float switch activates the pump.

3. Pump Turns On and Lifts Wastewater

The float switch sends power to the sewage ejector pump, causing it to turn on. It then pumps the wastewater out of the sump pit up to the elevation of the sewer line.

4. Wastewater Flows to Sewer by Gravity

Once lifted by the pump, the wastewater enters the sewer line where it can then flow downwards by gravity again to the municipal sewers or a septic tank.

5. Float Switch Turns Pump Off at Low Level

As the pump evacuates the sump pit, the water level drops. When it reaches a preset low level, the float switch cuts power to the pump, turning it off again until the next cycle.

Sewage Ejector Pump System Components

A complete sewage ejector pump system contains the following components:

Sewage Ejector Pump

The pump itself is the core of the system. Most residential systems use a 1/2 hp to 3/4 hp centrifugal or submersible sewage pump capable of at least 15-20 feet of head pressure. It needs to be powerful enough to push waste fully to the sewer line.

Sump Pit

This is the holding tank that collects the wastewater before it is pumped out. It needs to be large enough to hold water during peak usage periods. The pit contains a strainer to filter out solids and debris before reaching the pump.

Float Switches

Float switches activate the pump at preset water levels and turn it off when the pit is empty. There must be a high level “on” switch and a lower level “off” switch.

Check Valve

The check valve allows water to flow in one direction only, preventing backflow of wastewater into the sump pit after it’s pumped out.

Pipe and Fittings

Piping runs from the fixtures to the sump pit, from the pit to the sewer line, and a vent pipe. Necessary fittings vary based on site layout.

Sewage Ejector Pump Types

There are two main classifications of sewage ejector pumps: pedestal pumps and submersible pumps.

Pedestal Sewage Ejector Pumps

Pedestal pumps contain the pump motor mounted above the sump pit. The pump itself sits at the bottom of the pit. The motor and electrical components remain dry while the pump submerges in the wastewater.

Submersible Sewage Ejector Pumps

In submersible ejector pumps, the pump motor and all electrical components are sealed inside a watertight casing that allows the entire unit to be submerged in the sump pit. The casing protects the internal parts from water damage or electrical shorts.

Submersible pumps are more expensive but usually preferred because the submerged design allows for more compact installation and keeps noise to a minimum.

Sizing a Sewage Ejector Pump

Proper sizing of the sewage ejector pump is crucial for it to work effectively. The steps involved include:

Calculate Total Fixture Flow Rate

Add up the flow rates for all fixtures that will drain to the ejector pump based on the drainage fixture unit values in the plumbing code.

For example, a toilet may be 4 DFU, a sink 2 DFU each. Sum the DFUs for all fixtures.

Determine Required Pump Capacity

Choose a pump capable of handling 1.5 times the total DFU. This provides extra capacity as needed.

Calculate Total System Head

Factor in the vertical lift needed to reach the sewer line along with head losses through the piping, elbows and fittings. Ensure the pump can supply the required total system head.

Choose Appropriate Pump Size

Select a pump model that meets the capacity and head requirements calculated. Allow for some safety margin.

Proper sizing will ensure the pump can keep up with maximum waste volumes without burning out or becoming overwhelmed. An undersized pump will lead to wastewater backups.

How to Install a Sewage Ejector Pump

Installing a sewage ejector pump system is an advanced plumbing project best left to professionals. However, here is an overview of the basic process:

1. Install Sump Pit

The sump pit may be pre-formed plastic or built from concrete, fiberglass or other material. The basin is buried in the basement floor or set into the ground if outside.

2. Set Float Switches

Install float switches at appropriate heights in the sump pit. The upper switch should activate the pump before the pit overflows.

3. Mount Pump

Set the pump unit in place at the bottom of the sump pit. The base must be level and even.

4. Connect Piping

Run drainage pipe from the fixtures to the sump pit inlet. Install PVC or ABS pipe from the pump discharge up to the sewer line.

5. Install Check Valve

The check valve assembly mounts between the pump and discharge piping to prevent wastewater from flowing back into the sump pit.

6. Vent System

The sewage ejector pump requires a vent to prevent air locks. The vent line should rise above flood level before turning downstream.

7. Electrical Hookup

The system needs a grounded power source. The pump is wired to switch on via the float switch. Consider a backup power source.

8. Test Operation

Fill pit with water and verify proper pump activation at preset levels. Check for leaks throughout system.

Sewage Ejector Pump Maintenance

Routine maintenance keeps sewage ejector pumps operating smoothly:

  • Inspect – Check sump pit regularly for leaks, debris buildup, float switch function. Look for signs of pump wear or damage.
  • Clean Debris – Remove any debris like grease, hair and grit from the sump pit strainer. Prevent buildup.
  • Check Discharge – Ensure water flows freely from the vent once the pump runs. Vent blockage causes air lock.
  • Test Switches – Manually activate float switches periodically to confirm proper operation. Replace worn floats.
  • Pump Test Run – Run pump briefly in manual mode quarterly to verify performance. Watch for problems.
  • Backup Power – If pump relies on a backup power source like a generator or battery, test backup system regularly.
  • Service Pump – Have a qualified plumber service the pump annually. Replace worn parts, lubricate seals, inspect electrical contacts.

Troubleshooting Sewage Ejector Pumps

Some common sewage ejector pump problems and troubleshooting tips:

Pump Won’t Start

  • Check circuit breaker – Reset if tripped
  • Inspect float switches – Clean/adjust floats, replace if defective
  • Test pump in manual mode – Bypass switch to isolate issue
  • Check control panel – Replace bad capacitor or relay

Pump Runs But Doesn’t Pump

  • Clear blockages – Remove debris clogging impeller
  • Check discharge pipe – Clear obstacles, vent blockages
  • Replace worn impeller – Impeller vanes must be intact

Pump Runs Continuously

  • Adjust float switch – Ensure enough vertical distance between floats
  • Check for backflow – Clean/replace check valve if stuck open
  • Examine for leaks – Repair any leaks in sump pit causing excessive flow

Pump Cycles On/Off Frequently

  • Enlarge sump pit – Increase holding capacity to reduce cycles
  • Check float switch – Adjust to wider vertical spread
  • Balance drainage lines – Even out flows to sump pit

Pump is Noisy

  • Ensure base is level – Re-align pump if mounting is uneven
  • Check for debris – Remove foreign objects stuck in mechanism
  • Lubricate bearings – Bearing wear causes excessive noise
  • Replace worn impeller – Damaged impellers create vibration

By inspecting the system thoroughly and isolating specific problems, most sewage ejector pump troubles can be repaired. Professional servicing may be needed for motor electrical or major component replacement.

Sewage Ejector Pump FAQs

Here are answers to some frequently asked questions about sewage ejector pumps:

Where are sewage ejector pumps used?

Sewage ejector pumps are used where gravity drainage alone cannot remove wastewater. This includes basement fixtures below sewer level and long horizontal drain runs that lack adequate downward slope.

How deep should a sewage ejector pit be?

Typical sump pit depth is around 24-36 inches. The pit must be deep enough to allow for the vertical distance between the pump’s on/off float switches.

Can you flush toilet paper with a sewage ejector pump?

Yes, toilet paper and all typical household wastewater can be pumped by a sewage ejector system. However, non-degradable items like wipes should be avoided.

Do sewage ejector pumps require venting?

Proper venting is critical to prevent air locks in the system. The vent line should rise vertically before turning downward to the sewer connection.

What kind of power source do sewage ejector pumps need?

Sewage ejector pumps usually run on standard 120V household electrical current. They may be plugged into a wall outlet or hard wired. Backup power should also be considered.

How do you prime a sewage ejector pump?

Submersible pumps self-prime on startup. Pedestal pumps may need to be manually primed by filling the suction pipe with water before initial use to facilitate siphoning.

Should a sewage ejector pump run continuously?

No, the pump should turn on based on float switch activation, run briefly to empty the sump pit, then turn off again. Continuous operation indicates a problem.

How often should sewage ejector pumps be serviced?

Pump manufacturers typically recommend professional maintenance every 1-3 years. DIY tasks like debris removal and float testing should be done every 6 months.

Can a sewage ejector pump be used with a septic tank?

Yes, sewage ejector pumps can help transfer wastewater to septic drain fields at higher elevations that otherwise could not drain by gravity alone.


Understanding how sewage ejector pumps work allows proper installation and maintenance for reliable service. When gravity drainage is not possible, they provide a critical pumping solution to lift and remove wastewater. By equipping your home with a adequately sized system and performing routine care, a sewage ejector pump will provide many years of trouble-free operation. Speak to a professional plumber if you have any concerns about implementing this important plumbing fixture.