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Water from a toilet, shower or kitchen located below the level of the sewer does not flow away by itself: a pump must lift it. The right equipment depends on what the water contains (solids, paper, grease), how you remove it (continuously or from time to time) and whether you already have a tank or a pit. Here is how to choose without mistakes.
Which water, which pump family?
The first criterion is the nature of the water to remove. A clean-water pump clogs quickly with solids; conversely, a sewage pump accepts large solids but is not made for fine abrasive sand.
| Water to remove | Pump family | What to check |
|---|---|---|
| Clean or very slightly loaded water (flooded cellar) | Cellar pump | Particle passage and float control, stated on the product page |
| Mud, sand, leaves, site water | Loaded water pump | Size of particles accepted, type of impeller |
| Domestic waste water: toilet, shower, kitchen, pit | Sewage pump | Free passage (in mm), vortex impeller, power supply |
| Toilet or sanitary fittings with a small-diameter pipe | Macerator pump or micro-station | Cutting system, discharge diameter |
| Permanent drainage of a home or premises | Lift station (one pump or two pumps) | Tank volume, number of pumps, alarm |
Free passage: the criterion that prevents clogging
The free passage is the maximum size of a solid that the pump lets through without jamming. It is given in millimetres on each product page. The more solids the water contains (toilet, torn wipes, grease), the larger it must be. A cellar pump, whose free passage is small, clogs quickly on waste water.
Vortex impeller or grinder?
- Vortex impeller: the impeller is set back from the flow, so the liquid and the solids go around it. It gives a large free passage and limits clogging, without cutting the solids. The discharge pipe must then be wide enough.
- Grinder (cutting system): the pump breaks up solids before pumping them. It lets you use a smaller-diameter pipe, useful when the route is long or constrained. See macerator pumps and lifting micro-stations.
Single pump, lift station or micro-station?
A sewage pump goes in an existing pit or tank. If you have no tank, a single-pump lift station supplies the tank, the pump and the level control. With a two-pump station, the pumps work in turn and the second takes over if the first fails: preferable when a failure cannot be tolerated. For small volumes, the micro-station has a built-in grinder.
Sizing: flow, head and pipe
Two values are enough to read a pump curve: the flow to remove and the total dynamic head (TDH), that is the height between the pump and the discharge point, plus the pipe friction losses (length, diameter, bends). The calculation is detailed in the guide calculating total dynamic head. The pipe diameter depends on the model: the product page states the discharge connection and the free passage; see choosing a hose or pipe.
The mistake to avoid
Fitting a cellar pump or a clean-water pump on waste water: the impeller jams or wears, and the pump fails. Another common omission: the non-return valve, without which the water in the pipe flows back into the tank at every stop.
Installation in brief
- Place the pump vertically at the bottom of a pit or a tank, on a stable surface.
- Fit a non-return valve on the discharge and a float or level probe to control the pump.
- Connect the discharge to an authorised outlet (local sanitation rules).
- Power the pump single-phase or three-phase according to the model, with residual-current protection, and follow the manufacturer’s instructions.
The 5-step selection method
- Identify the water: clean, loaded or waste water with solids.
- Choose the free passage or the grinder according to the solids and the pipe diameter available.
- Decide single pump, lift station or micro-station depending on whether you have a tank.
- Calculate the flow and the TDH from the pipe route.
- Check the electrical supply, the non-return valve, the level control and the authorised outlet.
Frequently asked questions
Can a cellar pump remove waste water?
No: its free passage is too small for solids and it would clog. Choose a sewage pump or a grinder pump.
What is a vortex impeller?
A vortex impeller is set back from the flow: the liquid and the solids go around it. It gives a large free passage and limits clogging.
Sewage pump or grinder pump?
A sewage pump with a vortex impeller lets large solids through without cutting them and needs a wide enough pipe. A grinder pump cuts the solids and accepts a smaller-diameter pipe. The choice depends on the solids and the pipe route.
Which pipe diameter for a sewage pump?
It depends on the model: the product page states the discharge connection and the free passage. A grinder lets you use a smaller-diameter pipe. See choosing a hose or pipe.
How do I install the pump?
Place it vertically at the bottom of a pit or a tank, with a non-return valve and a float or level probe. Follow the manufacturer’s instructions.
Do I need a lift station?
Yes if you have neither a pit nor a tank: the station supplies the sealed tank, the pump and the level control. With two pumps, the second takes over if the first fails. See the lift stations.
Going further
Choosing a sewage pump stationOne or two pumps, tank, lifting height.Sewage pumpsSubmersible pumps with a large free passage, domestic and industrial.Lift stationsTank, pump and level control supplied together.Choosing a lift pumpClean, loaded, waste water: which pump family.Calculating TDHHead, friction losses and reading the curve.Choosing a hose or pipeDiameter, discharge and pipe type.