Joining Cast Iron and Plastic Soil and Vent Pipe: A Simple Guide

Are you faced with the challenge of connecting a new plastic waste pipe to an old cast iron one? This is a common issue that many homeowners encounter when undertaking plumbing renovations. In this article, we will explore the reasons behind the use of cast iron in drainage systems, the options available for connecting to cast iron pipes, and step-by-step instructions on how to make the connection.

Why Choose Cast Iron for Drainage Pipes?

Cast iron has been a popular choice for drainage pipes and other structures for many years. Its durability, strength, and resistance to damage make it ideal for exposed areas, such as soil pipes and guttering. If your property is old enough, it may still feature some cast iron elements. However, modern PVC pipe is now the preferred option for plumbing purposes.

Can You Remove Cast Iron Pipes?

Yes, you can remove old cast iron pipework and replace it with PVC pipes. However, it is important to consider whether it is necessary. If the existing pipe is in good condition and there are no changes to the plumbing layout, there may be no need to undertake the work. Cast iron pipes can last for many years, and replacing them would be a waste of time and money.

Options for Connecting to Old Cast Iron Pipes

If you do need to remove cast iron pipework, there are several options available for connecting to the old pipes. These connectors allow you to seamlessly join your new PVC pipework to the existing cast iron or clay pipes.

110mm Universal Pipe Connector/SP140 Connector

The 110mm universal pipe connector, also known as SP140 connector, is a versatile solution for connecting new PVC soil pipes to older pipes, including cast iron and clay. After cutting the old pipe, the finned end of the connector is pushed into the cut pipe, creating a modern push-fit socket for the new pipework. It provides a firm and secure fixing while ensuring a leak-free seal.

Flexible Pipe Connector

The flexible pipe connector is a rubber adaptor that is placed over the cut iron or clay pipe and secured with a compression clip. The new PVC pipework is then connected to the top of the adaptor, ensuring a tight seal. These connectors are effective and can be used both above and below ground, although they may not be aesthetically pleasing when used above ground.

Timesaver Coupling

The Timesaver coupling is a type of pipe joiner designed for connecting older diameter pipework to newer 110mm PVC pipes. It is known for its strength and secure connection. The Timesaver coupling is available in versions for both above-ground and underground use. It is a popular choice for joining pipes underground due to its durability.

How to Connect to Cast Iron Drainage Pipes

Now that we have explored the reasons and options for connecting to cast iron pipework, let’s look at the step-by-step process of making the connection.

Isolate any Water or Waste Flow

Before starting any work, ensure that the water or waste flow is isolated to prevent any unexpected spills. Cover toilets connected to the soil pipe and place out-of-order signs. If you are working on guttering, choose a dry day to avoid rainwater flow.

Cut Away Existing Pipe

Using an angle grinder or reciprocating saw with a metal blade, cut the existing cast iron pipe approximately 4-6 inches above ground level. Make sure to mark a level cutting line to ensure a straight cut. Wear protective clothing, a mask, gloves, eye protection, and face protection to guard against dust and debris.

Remove Old Cast Iron Pipework

After cutting the pipe, remove any brackets holding the cast iron pipework in place. Some brackets may be screwed, while others may require leveraging with a pry bar. Keep in mind that cast iron pipework is heavy, so it may be necessary to enlist help to maneuver it.

Fix Pipe Connector to Cast Iron

Depending on the type of connector being used, place it either in or over the top of the cut pipe tail protruding from the ground. Push the connector firmly into or over the pipe tail, ensuring it sits correctly. Use the appropriate tools to tighten the connector securely, depending on the connector type.

Connect New Pipework

Push the new pipe into the top of the connector, ensuring a secure fit. If using a universal connector, apply some washing up liquid around the seal to aid insertion. If using a flexible connector, wiggle the pipe into place, using washing up liquid if needed. For Timesaver couplings, carefully insert the pipe, taking care not to damage the seal. Once the pipe is in place, secure it with brackets on the wall.

Test for Leaks

Once the pipework is secure, check for any leaks by running water through the system. Ensure that all connections are watertight and fix any issues as necessary.


Connecting new plastic pipework to cast iron pipes may seem like a daunting task, but with the right connectors and proper techniques, it can be straightforward. The options available, such as universal connectors, flexible pipe connectors, and Timesaver couplings, provide effective solutions for joining different types of pipes.

Remember to take the necessary precautions, isolate water or waste flow, and use appropriate tools and safety gear during the process. By following these steps, you can successfully connect your new plastic pipework to existing cast iron drainage pipes.