How to Connect 110mm Drainage Pipes to Soil and Waste Systems

When connecting 110mm drainage pipes to soil and waste systems, it’s important to know that soil pipes, soil stacks, and soil vent pipes are all the same size.

This means they are compatible, and the connection process is simple once you understand the correct method.

Here's how to do the job properly without complications or misunderstandings.

1. Measure and Cut the Pipes

First, measure the length of the pipe required for the installation.

Cut the pipe using a fine-toothed saw for a clean and straight cut.

Once cut, smooth the edge of the pipe with a chamfer tool or file.

This step ensures the pipe fits smoothly into the coupling or socket and protects any rubber seals from damage.

2. Select the Correct Connection Method

Push-fit couplings and Solvent welding are the main methods for connecting 110mm pipes. Both work for soil and drainage systems.

• Push-Fit Coupling: This is the simplest method for DIY installations. Push-fit couplings come with a rubber seal that secures the pipe in place. Simply push the chamfered end of the pipe into the coupling until it meets the stop. It’s quick and requires no adhesive or special tools, making it ideal for most household applications.
• Solvent Weld: For a more permanent, durable connection, especially in heavier-use systems, use solvent weld. Apply solvent cement to both the outside of the pipe and the inside of the fitting, then push the pipe in fully and hold for a few seconds. This creates a bond that will harden and provide a completely watertight connection. Note: This system is gravity-fed, so there’s no high pressure involved. The focus is on making a secure, long-lasting connection, not pressure resistance.

3. Connecting to the Soil Stack or Waste System

• For connections to a soil stack (the vertical pipe that handles waste from toilets and other appliances), ensure the pipe is pushed fully into the stack connection and sealed properly. Remember, soil pipes, stacks, and vent pipes are the same size, so the connection should fit easily.
• For waste systems (such as kitchen sinks, washing machines, or showers), you’ll need to connect smaller waste pipes (32mm or 40mm) into the larger 110mm soil pipe. To do this, use a Boss Pipe or Strap-on Boss, along with a Boss Adaptor. These fittings allow smaller waste pipes to drain into the main soil system. Make sure these connections are properly sealed to avoid leaks.

Important Note: You connect the waste pipe to the soil pipe, not vice versa. Waste flows into the larger soil system from the smaller pipes (e.g., sinks or baths).

4. Install Waste Traps

Waste traps should be installed in waste pipe systems to prevent unpleasant odours from returning through the pipes. Waste traps aren’t primarily for stopping blockages but rather for stopping smells. Watch our Installing Waste Pipes and Traps (Video) for a step-by-step guide to ensure proper installation at all appropriate points, like sinks and washing machines.

5. Connecting to Older Systems

If you’re working on an older home that uses cast iron soil pipes, you’ll need a Drain Adaptor to connect modern 110mm plastic pipes to cast iron systems. The Boss Adaptor mentioned earlier won’t work for this purpose, as it's designed for plastic-to-plastic connections, not cast iron.

6. Underground Installations

When installing pipes underground, ensure you follow these steps for a proper, compliant system:

• Slope the pipes correctly: The standard slope is 1:40, meaning for every 40 units horizontally, the pipe should drop by one unit. This allows for efficient drainage without the risk of water backing up.
• Backfill the trench: Once the pipes are in place, backfill them with gravel or pea shingle. This supports the pipes and helps prevent damage from ground movement.

This is a crucial part of underground drainage. For more information, you can read our article on Invert levels and falls & drains in drainage.

Final Tips

• Check for leaks: After connecting the pipes, test the system by running water through it to ensure everything is sealed and there are no leaks, particularly with solvent weld connections, which need time to cure.
• Ensure compliance: Check local building regulations to ensure your installation meets legal standards, especially for underground or main sewage system connections.