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Soil and Waste Pipes: Types, Differences and FAQs

13 January 2025

Soil and waste pipes are essential parts of any property, responsible for safely removing wastewater and sewage. 


Understanding the differences between soil and waste pipes, the types and how they operate will help you to maintain a functional and efficient drainage system. In this detailed guide, we’ll cover soil and waste pipe FAQs and offer maintenance tips. 

 

Pipe drainage on side of house Pipe drainage on side of house

What is a soil pipe?

Soil pipes, also known as soil vent pipes (SVP), carry sewage and waste from toilets, urinals and bidets. They ensure that dirty water is safely transported to the underground drainage system. 


Soil pipes run horizontally from your toilet to the soil stack, which is usually a vertical pipe in the outside wall or inside a wall cavity, connecting to your underground drainage system. At the top, the soil pipe will have a vent to release gases and maintain air pressure in the system.


Soil pipes are available in different materials:

  • UPVC: UPVC soil pipes are lightweight, affordable and resistant to corrosion. This is the most common choice for modern homes.
  • Cast iron: Cast iron soil pipes are strong and durable, often used in older properties. Cast iron pipes require more maintenance to prevent rust.


The standard soil pipe diameter in the UK is 110mm, which is wide enough to ensure efficient waste removal without blockages.


Soil pipe fittings include bends, connectors and couplings, enabling them to be installed around corners and obstacles.

 

  1. EDSBDS135B Aquaflow Black Double Socket 135° Soil Bend - 110mm
    £26.22 £21.85
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  2. SAFTB Aquaflow Black Triple Socket 92.5° Access Branch - 110mm
    £86.38 £71.98
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  3. EDSBSS92.5B Aquaflow Black Single Socket 92.5° Soil Bend - 110mm
    £14.98 £12.48
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  4. SSBPB Aquaflow Black Soil System Three Way Opening Short Boss Pipe - 110mm
    £10.03 £8.36
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What is a waste pipe?

Waste pipes are designed to carry wastewater from sinks, showers, baths and appliances like washing machines and dishwashers. Unlike soil pipes, waste pipes do not handle sewage.


Waste pipes are usually made from the following materials:

  • UPVC: UPVC waste pipes are affordable, easy to install and resistant to corrosion. They’re perfect for modern plumbing systems.
  • Copper: Copper waste pipes are sometimes used in older homes but are less common due to their cost and difficulty to install.


Waste pipes typically come in 32mm for basins; 40mm for sinks, baths and showers; and 50mm for larger systems or when multiple connections are needed. Fittings include traps, connectors, and bends to ensure water flow and prevent odours.

 

  1. SPE3MB Aquaflow Black Plain Ended Soil Waste Pipe - 110mm x Length 3m
    £35.92 £29.93
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  2. SPS3MB Aquaflow Black Single Socket Soil Waste Pipe - 110mm x Length 3m
    £37.91 £31.59
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  3. SPS3MW Aquaflow White Single Socket Soil Waste Pipe - 110mm x Length 3m
    £36.26 £30.22
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Soil pipe vs waste pipe

Although soil and waste pipes both handle water removal in homes, there are key differences between the two:

  • Purpose: Soil pipes carry sewage and wastewater from toilets (blackwater), while waste pipes carry wastewater from sinks, baths and other appliances (greywater).
  • Sizes: Soil pipes are generally 110mm and waste pipes are typically 32mm to 50mm.
  • Installation: Soil pipes require a vent to manage gases, but waste pipes connect directly to soil pipes or drainage systems.

Which pipe is better for sewage?

For carrying sewage, soil pipes are the only suitable option because of their larger diameter and venting requirements. Waste pipes are not designed to handle solid waste from toilets.

 

Why might you need to connect wastewater to a soil pipe?

In some instances, you may need to connect a waste pipe to a soil pipe, especially if space is limited or you don’t have direct access. For example, if your sink, bath or shower is near your toilet, or if they are on the first floor of a home, combining the pipes can streamline the plumbing system. 


To connect a waste pipe to a soil pipe:

  • Measure and cut: Ensure the waste pipe is cut to the correct length for the connection.
  • Fit a connector: Use a suitable connector, such as a boss connector, to join the waste pipe to the soil pipe.
  • Seal the connection: It’s vital that you ensure all connections are watertight to prevent leaks and odours.
  • Test the system: Run water through the waste pipe to check for leaks.

 

How deep should a soil waste pipe be buried?

In the UK, soil waste pipes should be buried at least 300mm in gardens or areas with no traffic. For pipes under driveways, the recommended depth is at least 600mm. This depth protects the pipes from damage caused by temperature changes or external pressure.

 

How to prevent blockages

Keeping your soil and waste pipes free from blockages is crucial to maintaining an efficient drainage system. Here are some of our top tips for preventing blockages:

  • Regular cleaning: Regularly flush your pipes with hot water to clear any buildup.
  • Install guards: Use leaf guards on guttering to stop debris from entering downpipes
  • Avoid flushing unsuitable items: Avoid flushing products such as wipes, nappies or sanitary products down the toilet.
  • Check traps: Ensure water traps in waste pipes remain filled to prevent odours.

 

How to build a solid system

A reliable drainage system depends on choosing the right pipes, fittings and installation techniques.

  • Use high-quality materials: UPVC soil and waste pipes are durable and low maintenance.
  • Ensure proper venting: Soil pipes must have vents to manage gases and pressure.
  • Professional installation: Hire a professional plumber to ensure the system is fitted and works correctly.


Understanding the difference between soil and waste pipes is essential to maintaining a functional drainage system. UPVC pipes are a reliable, cost-effective option for most UK homes. If you’re ready to upgrade, explore our range of drainage and waste products, and contact us today for more information.

FAQs


How much does a new soil pipe cost?

The cost of a new soil pipe depends on the material and length. On average, UPVC soil pipes cost between £20 and £50 per length, while cast iron pipes can cost £80 to £200 per length.

 

How far can a toilet be from a soil pipe in the UK?

A toilet can typically be up to six metres away from a soil pipe, provided the waste pipe has the correct gradient (at least one in 40).

 

Can a waste pipe be connected to a soil pipe?

Yes, waste pipes can be connected to soil pipes using suitable connectors. This is common in bathrooms where space is limited, or where the bathroom is not located on the ground floor.

 

What are the rules for external soil pipes?

External soil pipes must be properly vented above the roofline and securely fixed to the wall. Ensure they are compliant with UK Building Regulations.

 

What happens if a soil pipe is not vented?

If a soil pipe isn’t vented, gases can build up and create foul odours. This can also cause poor drainage and noises in your plumbing system.

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