Sewage pumps are used when gravity drainage is not viable. In most situations wastewater is designed and piped to flow downhill on its own, to the nearest manhole, which in turn flows downhill to the main sewer. However, if the toilet, shower or sink sits lower than the point it needs to discharge to, you need a pump to move it.
If you already know you need one, you can go straight to our range of sewage pumps. This guide explains when a sewage pump is needed, the main types and how to size one.
When do you need a sewage pump?
A typical example is a bathroom in a basement below the level of the sewer.
You would also require a pump where the "fall" or gradient on a pipe is not sufficient for gravity flow.
Without enough gradient, the flow will be insufficient, meaning blockages form and you will have continued problems. An example would be a garden office at the bottom of the garden. You might install a toilet and a sink, only to discover there is not enough fall to reach the main sewer, and so a pump would be required.
Typical UK gravity drainage falls (Building Regs and BS EN 12056) are:
- 100mm (110mm) foul drainage: recommended gradient is 1:40
- Minimum acceptable gradient is usually 1:80 if flows are adequate
What changes once a sewage pump is used
Once a sewage pump is doing the work, the discharge pipework becomes pressurised, so you no longer need to maintain a specific fall. Instead, you follow the pump manufacturer's guidance on the maximum vertical lift, the horizontal run, the pipe diameter and the number of bends allowed. This is where understanding pump curves matters, as you need to know both the flow and the head the pump will deliver. Our guide on how to read a pump curve explains this.
Tank size and flow rate must also match the number of toilets and users, and Approved Document H expects the receiving chamber to hold a full day's inflow from the building it serves. A system serving several properties will need a far larger tank than something serving a single washroom. To avoid issues later it is recommended that a consulting drainage engineer size and specify the tank and pump at the drainage design stage.
If the work involves a new drainage connection, you may also need a Section 106 agreement. Section 106 of the Water Industry Act 1991 gives you the right to connect foul or surface water drainage into the public sewer. Again, this is something a consulting drainage engineer should deal with for you. There is more on the rules in our guide to sewage pumps and building regulations.
Sewage pumps are usually automatic, either with an attached float switch or designed to work with a float inside a chamber. A sewage pump should always be automatic, so you do not end up manually monitoring tank levels. The pump will start when the chamber fills and stop once the liquid drops to the correct level.
Unlike puddle pumps, sewage pumps sit on a stand and have large openings that allow solids to pass through. They cannot pump down to low water levels because that would impact their solids handling ability. They must be set inside a chamber which collects liquid and solids, and when the level rises in the tank, the pump activates. Most sewage pumps use pendant float switches because other types, such as tube floats or sensors, are more likely to snag or clog.
The diagram below compares the openings of low level pumps with sewage pumps.
The three main types of sewage pump
- Vortex impeller pumps. These allow solids to pass through without obstruction. The EVAK Hippo 50 and Hippo 100 are good examples, giving a free passage of up to 50mm.
- Grinder pumps. These have a grinder which macerates the waste as it is pumped.
- Cutter pumps. Cutter pumps, such as the APP DSPK Cutter Sewage Pump, have a cutting blade similar to a blender. They chop solids into smaller pieces so the pump can move them more easily, which works well when dealing with fibrous or tough materials that would clog other pumps.
You can see the full range on our sewage pumps collection.
For a fuller comparison of vortex, cutter and grinder pumps, see our guide to choosing between a sewage, cutter or grinder pump.
Three example sewage pumps
Below are three example sewage pumps for different jobs. At the smaller end is the APP SV150 Auto, which has a maximum flow of 170 litres per minute and a maximum head of 5.7 metres. At the top end is the Speroni Cutty with a maximum flow of 400 litres per minute and a maximum head of 27 metres. In the middle is a packaged pump station which gives you everything you need for a garden room or similar setup.
1. A single washroom on a budget: APP SV150 Auto
Perfect for sewage and draining, the SV series of submersible pumps are manufactured by APP Pumps. They are a great range of submersible pumps that come with cast iron pump casings, vortex impellers and 304 stainless steel motor frames.
Head: 5.7m. Flow rate: 170 litres per minute.
A cast iron casing, recessed vortex impeller and 304 stainless motor frame pass soft solids up to 27mm without a cutter or grinder. Automatic on a pendant or tube float, 230V, with a 2-year warranty. Ideal for a single washroom or light foul drainage on a budget.
2. A garden room or annexe: FPS Iguazu Sump Foul Pro packaged station (Hippo 100)
The Foul Pro system uses the EVAK Hippo 100 Sewage Pump, providing increased flow and head performance compared with the standard model. This pump delivers a flow rate of up to 480 litres per minute and a maximum head of 11 metres, making it suitable for larger foul drainage systems or sites with higher discharge lifts.
3. Long distances or uphill through a small pipe: Speroni Cutty grinder pump
The Cutty series grinder pumps are of cast iron construction. They are used in sewage stations and for servicing individual houses, or groups of houses, where drainage by gravity is not possible. They are ideally suited to applications where effluent needs to be pumped over a long distance through a small bore pipe.
Head: 17 to 27m (model dependent). Flow rate: 340 to 400 litres per minute (model dependent).
A cast iron submersible grinder that shreds waste between a stainless cutting disk and impeller cutter, so it can pump through small-bore pipe over distance or uphill. The Cutty 200 has a maximum flow of 340 litres per minute and a maximum head of 17m; the Cutty 250 steps up to a maximum flow of 400 litres per minute and a maximum head of 27m. Available in 230V single phase or 400V three phase, with an optional guide-rail auto-coupling for permanent stations.
