Quick answer: If a toilet, shower or sink sits below the level of the public sewer, the drainage either has to be pumped up to it or protected against the sewer backing up. Approved Document H decides on surcharge risk: where the sewerage undertaker rates the risk high, the basement drainage should be pumped; where it is low, a double anti-flooding valve with a manual closure will do. Below sewer level a pump station is nearly always the answer, because a valve stops the sewer coming in but does nothing to get your waste out.
Basement bathrooms are the fastest growing type of sewage pump enquiry we get, from Victorian terraces with converted cellars to new build flats with a lower ground floor. The question is always the same: does this need a pump, or will a valve do? The regulations are clearer on this than most people expect, and the physics settles the rest.
Why basements get sewage back
Combined sewers, which carry foul water and rainwater in the same pipe, are designed to surcharge: in heavy rain the water level in the manhole rises above the top of the pipe. Any fixture below that level is the sewer's overflow. Approved Document H calls this flooding due to surcharge, and it is the reason the rules exist.
What the regulations say
For a basement containing sanitary appliances, the guidance is that the sewerage undertaker should be asked how likely surcharge is and how often. Where the risk is high, the drainage from the basement should be pumped. Where it is low, an anti-flooding valve should be installed on the drainage from the basement. The valve has rules of its own: it should be a double valve type suitable for foul water, with a manual closure device, normally serving one building, with a notice inside the building saying the drainage runs through a valve, where the manual override is and how to maintain it. Everything not affected by surcharge should bypass the valve and drain by gravity. For low-lying sites without a basement, an external gully set at least 75 mm below floor level is the first line, so that any flooding happens outside.
The pumping side of the document, which sets the standards for the station and the 24-hour storage rule, is covered in our guide to sewage pumps and the Building Regulations.
Valve or pump: the practical difference
An anti-flooding valve is passive. It lets your waste out and closes when the sewer tries to come back. It works, within limits: it needs the pipe between the basement and the sewer to fall by gravity in the first place, it has to be kept clean, and while it is closed nothing in the basement drains at all, which is why the regulations want a notice and a manual closure.
If the appliances are below the sewer, gravity has already failed. The waste cannot get to the sewer without being lifted, so a valve on its own solves the wrong problem. A pump station collects the basement drainage in a chamber, lifts it with a sewage pump up to a point above the level the sewer can surcharge to, and lets it fall into the drain from there. The rising main carries a non-return valve, and the high point of the loop is what protects the basement: the sewer would have to rise above it to get back in.
Choosing the station
Two decisions. First, inside or outside: a floor-mounted unit inside the building, built to BS EN 12050, or a below-ground chamber outside with the pipework brought to it. Inside units are compact; outside chambers are easier to service and keep the smell and the noise out of the house. Second, what it has to pass: a WC means a sewage pump with a free passage of at least 50 mm, so a vortex impeller, or a cutter where the rising main is long and small-bore; a shower or basin on its own can use a grey water station. Then the lift and the distance set the head, and the number of people set the storage.
Our 190 litre packaged stations cover the common cases: the Iguazu Foul with the EVAK Hippo 50 for a basement bathroom lifting up to 7 m, the Iguazu Foul Pro with the Hippo 100 where the lift or the run is longer, and the Iguazu FEKA with a stainless pump. Larger chambers, twin pumps and different inlet depths are built to order through our below-ground pump stations page; the full range of pumps is in the sewage pumps collection.
Keep groundwater and foul water apart
A converted basement often has two pumps: one for the Type C cavity drainage that collects groundwater, and one for the bathroom. They must never share a chamber. Groundwater into the foul station overloads it, and the regulations list misconnection of surface water to the foul sewer as a cause of the very surcharging you are trying to avoid. The basement waterproofing pumps handle the clean side; the sewage station handles the foul side; each has its own discharge.
Installation points that get missed
Vent the chamber to outside. Fit an isolation valve and a non-return valve on the rising main where they can be reached. Keep the control panel and the plug above flood level. Fit a high level alarm, because a failed pump in a basement bathroom shows itself as a flooded floor, not a warning light. Put a notice by the toilet about wipes: a vortex pump passes 50 mm solids, but a rag of wipes defeats anything. And service it annually, which for most stations means lifting the pump, clearing the float and checking the valve.
At a glance
| Situation | What the regulations point to | What we would fit | Notes |
|---|---|---|---|
| Basement WC and shower, sewer surcharges in storms | Pumped drainage | Iguazu Foul (Hippo 50) or Foul Pro (Hippo 100) | Rising main looped above surcharge level, non-return valve, alarm |
| Basement utility with a sink only, low surcharge risk | Anti-flooding valve | Double valve, foul rated, manual closure, notice inside | Only if the pipe still falls to the sewer by gravity |
| Lower ground floor flat, several appliances, lift over 7 m | Pumped drainage | Iguazu Foul Pro, or a bespoke chamber with a cutter pump | Size storage on 24 hours at 150 litres per person |
| Commercial basement that cannot close | Pumped drainage | Bespoke twin pump station | Duty and standby, alarm with battery, telemetry |
The notice and the manual closure are the part nobody fits
Where to go next
The standard chambers are in packaged pump stations, anything larger goes through the bespoke sizing page, and the pumps on their own are in sewage pumps.
We are happy to provide advice on the products we sell, with detailed product information and guidance available throughout our website. However, the purchase of a product does not include site-specific engineering advice, flood risk assessments or recommendations on the suitability of a particular solution for your property.
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