Which one you need depends on where the pipe is, what it’s carrying, and what size it is. Below we’ll go through both methods properly, plus how to join pipes of different sizes, connect new pipework to an existing system, and fix a joint that’s already leaking.

A word of caution up front: drainage connections that carry foul water are covered by Building Regulations (Approved Document H in England), and any new connection into an existing drain or sewer needs to be inspected by Building Control before you backfill the trench. Get the pipework right but skip that step, and you can end up having to dig it back up.

What You’ll Need

Before starting, gather:

Pipe cutter or fine-toothed hacksaw — for clean, square cuts
Deburring tool or file — to smooth cut edges
Chamfering tool (or a file/sandpaper for a manual chamfer)
Silicone-based pipe lubricant — never use petroleum jelly or washing-up liquid, both degrade rubber seals over time
Solvent cement and primer/cleaner (only for solvent weld joints)
Tape measure and marker pen
Spirit level — essential for underground runs, where gradient (fall) determines whether the system actually works
Appropriate pipe couplers, adaptors or repair collars for the job

How to Connect Drainage Pipes Together (Push-Fit Method)

This is the standard method for 110mm underground drainage, soil pipes, and most waste pipe systems using rubber ring seals.

Measure and mark the pipe. Cut to length allowing for the depth of the socket — measure how far the pipe needs to insert and mark this on the outside so you can check full engagement later.
Cut the pipe square. An angled cut won’t seat properly in the socket and is one of the most common causes of leaking joints. Use a pipe cutter where possible; a mitre box helps if you’re using a hacksaw.
Deburr and chamfer the cut end. Remove burrs with a file, then chamfer the edge at roughly 15° so it doesn’t snag or damage the rubber seal as it goes in.
Check the seal is seated correctly in the socket or coupler and isn’t twisted, split or perished. A damaged seal is the single most common reason a “correctly installed” push-fit joint still leaks.
Apply silicone lubricant to the chamfered pipe end and to the seal itself — not sparingly. This isn’t optional; forcing a dry pipe into a seal can roll or damage the rubber even if the joint looks fine afterwards.
Push the pipe fully home, then withdraw it by around 10mm (check manufacturer guidance — this is usually specified and marked with a witness line on the pipe). This gap allows for thermal expansion; a joint pushed in too far and left with zero clearance can crack under expansion in hot weather.
Check alignment and support. The pipe should sit straight, unstrained, and be supported at the intervals your pipe manufacturer specifies — unsupported pipe runs sag over time and joints take the strain.

How to Connect PVC Drainage Pipes Without Leaks (Solvent Weld Method)

Solvent weld is chemical welding, not gluing — the solvent softens the surface of both pipe and fitting so they fuse into a single piece as it cures. Done correctly it’s stronger than the pipe wall itself; done badly, it’s one of the most common sources of an intermittent, hard-to-trace leak.

Dry-fit first. Push the pipe into the fitting without solvent to check it seats correctly and mark the insertion depth.
Clean both surfaces with the manufacturer’s cleaner/primer — this removes surface grease and slightly softens the plastic, and skipping it is the most common reason a solvent weld joint fails.
Apply solvent cement evenly to the outside of the pipe and the inside of the socket. Don’t overload it — excess cement pools inside the pipe and can restrict flow or weaken the joint.
Push the pipe fully in with a slight twist, then hold firmly for around 30 seconds while the joint sets.
Wipe away any excess cement immediately.
Leave undisturbed for the cure time stated on the product — typically a few minutes for handling, but full cure and pressure-testing should wait 24 hours.

Do drainage pipes need to be glued? No — only smaller-bore waste pipe generally uses solvent weld. Underground drainage and soil pipe almost always uses push-fit rubber ring joints specifically because they need to flex slightly with ground movement; a rigid glued joint underground is more likely to crack than to hold.

Connecting Different Size Drainage Pipes

You can’t force a smaller pipe into a larger socket and expect a watertight result — you need a reducer, or a flexible coupling that’s rated to bridge the size (and often material) difference.

Same material, different diameter: use a manufacturer reducer/reducing coupler.
Different material (e.g. old clay or cast iron to new uPVC): use a flexible rubber coupling with stainless steel clamps, or a purpose-made adaptor fitting for that material combination.
Rule of thumb: for domestic foul drainage, 110mm is standard; 160mm is used for shared or higher-capacity runs. Never reduce pipe size in the direction of flow on a foul drain, as this increases the risk of blockages.

Connecting a New Drain Pipe to an Existing System

This is one of the most searched variations of this task, and it’s also the one with the most regulatory weight attached.

Expose the existing pipe carefully, without disturbing its bedding or gradient.
Identify the material — PVC-U, clay, cast iron and pitch fibre all need different connection approaches.
Cut in a saddle junction, or cut the pipe and insert a proper junction fitting — never just butt two pipes together and seal the gap with cement or expanding foam. It will fail.
Match or improve the gradient through the new section — a badly angled new connection is one of the most common causes of blockages soon after installation.
Notify Building Control before backfilling. For any new connection into an existing drain or public sewer in England, this is a Building Regulations requirement under Approved Document H, and it needs inspecting before the trench is covered over — not after.

How to Connect Underground Drainage Pipes Around Corners

Never rely on a tight bend or force a straight pipe into an angle it wasn’t designed for. Use the correct-degree bend fitting (commonly 45° or 90° for 110mm systems) and, where a run changes direction and is not accessible, install an inspection chamber at the change of direction — this is both good practice and, in many cases, a Building Control expectation, since it gives future access for clearing blockages without digging up the pipe run.

How to Repair a Leaking Drainage Pipe Connection

If an existing joint is leaking, the fix depends on the cause:

Symptom	Likely Cause	Fix
Leak appears after cold weather	Joint pushed fully home with no expansion gap	Reset joint with correct withdrawal clearance
Leak at a push-fit joint under load/movement	Perished or displaced rubber seal	Replace seal, relubricate, reseat
Leak at a solvent weld joint	Poor surface prep or insufficient cement coverage	Cut out and replace the section — solvent welds can’t be reliably “topped up”
Persistent seepage, damp patch, or smell underground	Cracked pipe or failed underground joint	CCTV drain survey to pinpoint the exact location before digging

For anything below ground where you can’t see the joint directly, guessing where the leak is usually costs more than diagnosing it properly. This is where a CCTV drainage inspection earns its cost back — it pinpoints the exact failure point so you’re not digging up three metres of garden to find a 20cm problem.

Common Mistakes We See on Site

Skipping the deburring step — sharp edges damage seals immediately or over time
Using the wrong lubricant, or none at all, on push-fit seals
Not allowing for expansion on push-fit joints, especially on long external runs
Butt-jointing old and new pipe without a proper coupling, then relying on sealant to bridge the gap
Ignoring gradient — a pipe that’s dead level or has a reverse fall will hold standing water and silt, leading to recurring blockages regardless of how good the joint itself is
Backfilling before inspection, on jobs that legally require Building Control sign-off

When to Call a Professional

DIY pipe joining is realistic for straightforward waste pipe repairs and simple above-ground extensions. It gets considerably riskier once you’re dealing with:

Underground drainage connecting to a shared or public sewer
Any job requiring Building Control notification
A leak you can’t visually locate
Persistent blockages after a repair (often a sign the underlying connection, not just the joint, is at fault)
Commercial premises, where a failed connection can mean contamination risk or a shutdown

If you’re in London and the job has moved from “fix a joint” to “something’s wrong with the drain and I can’t see what,” that’s exactly the point to bring in a CCTV drain inspection or a professional drainage service rather than keep digging. And if it’s actively flooding, backing up, or you’ve hit a burst while working on it, our 24/7 emergency plumbers can be on site fast rather than left to worsen overnight.

FAQs

What is the best way to connect drainage pipes?
For underground and soil drainage, push-fit rubber ring joints are the standard and preferred method in the UK, because they allow for ground movement and thermal expansion. Solvent weld is used mainly for smaller waste pipework above ground.

What fitting is used to join drainage pipes?
Couplers for straight joins, reducers for different diameters, bends for changes in direction, and adaptors for connecting different pipe materials (e.g. clay to PVC).

Can you connect two different size drain pipes?
Yes, using a reducing coupler if the materials match, or a flexible rubber coupling with clamps if you’re bridging different materials or larger size differences.

How do you stop a drain pipe connection from leaking?
Cut pipes square, deburr and chamfer the ends, use the correct lubricant on push-fit seals (or correct cleaner/cement for solvent weld), and always allow the manufacturer’s specified expansion clearance on push-fit joints.

Can you connect a new drain pipe to an existing one?
Yes, but for foul drainage this typically requires Building Control notification and inspection before the connection is backfilled — this isn’t optional for compliant work in England.

How to Connect Drainage Pipes Together: A Complete Guide