How Sewage Ejector Pumps Work

Washing machine and dryer in a laundry room

Hero Images / Getty Images

A sewage ejector pump, also called a pump-up ejector system, is used when a bathroom, laundry room or any other type of plumbing fixture is located below the level of the main sewer or septic line flowing from the house. The flow of drain-wastewater depends on gravity, so any plumbing systems in which fixtures are located below the level of the main sewer line all require a pump or some means of elevating the wastewater so it can flow down and out properly.

What Is a Sewage Ejector Pump?

The principle of a sewage ejector pump is similar to how a groundwater sump pump operates, but instead of rainwater seepage being pumped out of the home, it is waste/sewage being lifted up and out into the main sewer lines or septic field.

Ejector Pumps in Homes

Most commonly, ejector pumps are used in homes with basement bathrooms or laundry rooms. Not all basements require them, but when the municipal sewer lines running to the street are at a higher level than the fixture, the ejector pump serves to pump both liquids and solids up into the sewer line so it can flow properly. Ejector pumps are also very common in septic drain-field systems, such as are found in rural locations where the septic drainage field or holding tank may be considerably higher than basement plumbing fixtures.

Sewage ejector pumps are meant to sit in a sump basin that is cut and dug into the ground below grade. This sump basin collects and holds about 30 gallons of waste, on average, for a moderate-sized home. The drain lines from the various fixtures in the basement area are sloped down into the side of the sump basin, and when the level of wastewater in the sump basin reaches a certain height, a moveable float on the sewage ejector pump starts the pump. The wastewater is then pumped out of the basin and up to the level of the sewer or septic line. Once the level in the basin goes down, the float drops back down and turns off the pump until the next time the basin fills.

System Requirements

A vent is required for a sewage ejector pump installation to equalize pressure during pumping and to provide an outlet for sewer gasses. The vent comes out of the sump pit and is either connected to an existing vent (soil) stack or runs up and through the roof.

The outlet pipe leaving the sewage ejector pump is usually 2 to 4 inches in diameter, connecting to the 3- to 6-inch main sewer line. Between the pump outlet point and the junction with the main sewer line, there is always a check valve to make sure that nothing drains back into the sump basin after the wastewater is pumped out. When it is installed properly, the top of the sump basin is sealed so that no waste or smell can come out of the top of the basin.

Planning Considerations

Before starting a project that requires the installation of a sewage ejector pump, it is a good idea to check with your local building department. Different communities may have unique plumbing and building codes and permit requirements. Any work involving septic or sewer lines is likely to require a permit, and with good reason, since improper installation can result in quite a mess. To be safe, find out what is required to install a sewage ejector pump legally before you begin. Get an estimate from a licensed plumber before deciding to do this project yourself, as this is a fairly advanced project for a DIYer.

Another thing to consider carefully is the size of the ejector pump you will need. Pumps come in various sizes (horsepowers), and the basins are available in different hold capacities. For the average residential installation, a standard pump kit with a 1/2 to 3/4 horsepower motor and 30- or 40-gallon is usually enough, but you can compare prices, specifications, and features to make sure you pick the system appropriate for your project.

Prices for the kits typically run from about $400 to nearly $1,000. This is not an installation you want to repair, though, so make sure you buy quality equipment that is large enough for your home. Sewage ejector pumps are available at local home improvement stores, online, and through your local plumbing supply house. They are also available for commercial applications, but these require a much larger sump basin.