The Complete Guide to Pipe Fittings and Connectors — Joining Pipes Securely Without a Plumbing Qualification

Why Understanding Pipe Fittings Matters

Most homeowners never think about pipe fittings until something leaks. Then they discover that the fitting under the sink is a compression joint that needs a new olive, or that the pipe behind the washing machine uses a push-fit connector that has worked loose, or that the threaded connection on the radiator valve needs PTFE tape. Knowing what type of fitting you are looking at, how it works, and how to maintain or replace it gives you the ability to handle minor plumbing issues immediately — and to communicate clearly with a plumber about larger ones.

Fittings are also the components you need to understand if you want to carry out straightforward plumbing tasks yourself: replacing a tap, connecting a washing machine, fitting an isolation valve, or extending a pipe run to a new appliance. These are tasks well within the capability of a competent homeowner, and the fittings are the key to doing them correctly and leak-free.

The Pipes in Your Home — Copper, Plastic, and What Connects to What

Copper pipe is the traditional material for domestic hot and cold water supply. It is strong, corrosion-resistant, and has a proven track record spanning decades. The standard sizes in domestic plumbing are 15 mm (for most supply runs to taps, radiators, and appliances) and 22 mm (for larger supply runs to baths, cylinders, and boilers). Less common sizes include 10 mm (for some tap and radiator connections) and 28 mm (for main supply and boiler connections).

Plastic pipe (typically polybutylene or cross-linked polyethylene, known by trade names) is increasingly used for domestic water supply. It is flexible, lightweight, resistant to freezing damage, and faster to install than copper. It uses the same 15 mm and 22 mm sizing as copper and connects with push-fit or compression fittings (with a pipe insert to support the plastic pipe inside the fitting).

Waste pipe (for drains from sinks, basins, baths, and showers) is almost always plastic — typically 32 mm for basin waste and 40 mm for bath, shower, and kitchen sink waste. Waste fittings use push-fit solvent-weld or compression connections.

The critical rule: Use fittings designed for the pipe material and size you are connecting. A 15 mm copper compression fitting is designed for 15 mm copper pipe. Using it on a different size or material without the correct adapter or insert risks a leak.

Compression Fittings — The Reliable Standard for Copper Pipe

Compression fittings are the most widely used method for connecting copper pipes in domestic plumbing. They require no heat, no specialist tools, and no adhesives — just two adjustable spanners and the fitting itself.

How they work: A compression fitting consists of three parts: the body (the main fitting with internal threads), the olive (a small brass or copper ring that sits around the pipe), and the compression nut (which screws onto the body). The pipe is inserted into the fitting body, the olive sits around the pipe at the mouth of the fitting, and the nut is tightened onto the body. As the nut tightens, it compresses the olive against the pipe and into the fitting body, creating a watertight seal.

Installation: Cut the pipe squarely using a pipe cutter (not a hacksaw, which produces a rough cut). Remove any burrs from the cut end. Slide the nut onto the pipe, then the olive. Insert the pipe fully into the fitting body. Hand-tighten the nut onto the body, then tighten with a spanner — typically one full turn past hand-tight, while holding the fitting body with a second spanner to prevent it from rotating.

The olive is the sealing element. If a compression joint leaks, the most common cause is an olive that has not been compressed sufficiently (undertightened) or has been deformed by overtightening. A correctly tightened olive creates a permanent deformation around the pipe that seals against the fitting body.

Compression fittings work on both copper and plastic pipe. When using plastic pipe, a pipe insert (a rigid metal or plastic sleeve) must be placed inside the pipe end before the fitting is assembled. The insert supports the pipe wall and prevents it from collapsing under the compression force. Without the insert, the olive crushes the soft plastic pipe rather than sealing against it.

Advantages: No heat required. Can be assembled and disassembled. Compatible with copper and plastic pipe. Reliable and well-proven. Available in every size and shape.

Disadvantages: Bulkier than soldered fittings. Slightly more expensive per fitting than capillary (soldered) fittings. The olive cannot be reused if the fitting is disassembled — a new olive is needed.

Push-Fit Connectors — Fast, Tool-Free Connections

Push-fit connectors (also called push-fit fittings or quick-connect fittings) are the fastest and simplest method of joining pipes. You push the pipe into the fitting, and an internal mechanism — a combination of a grab ring (which grips the pipe and prevents it from pulling out) and an O-ring (which creates the watertight seal) — locks the pipe in place.

No tools are required for assembly. Cut the pipe squarely, deburr the end, mark the insertion depth on the pipe, and push the pipe firmly into the fitting until it reaches the internal stop. The connection is made.

Disassembly is equally straightforward. A release collar or clip on the fitting is pressed or twisted while the pipe is pulled out. This makes push-fit fittings ideal for temporary connections, testing layouts, and situations where the plumbing may need to be reconfigured.

Push-fit fittings work on copper and plastic pipe. When used with plastic pipe, a pipe insert (stiffener) is inserted into the pipe end to support it — the same principle as with compression fittings on plastic pipe.

Advantages: No tools required. Fastest assembly method. Can be disassembled and reused. Work on copper and plastic pipe. Ideal for homeowners who are not confident with compression or soldered joints.

Disadvantages: More expensive per fitting than compression or soldered alternatives. Bulkier than compression fittings. The O-ring seal can deteriorate over many years (particularly in hot water systems where the rubber is subjected to continuous heat). Not all plumbers consider them suitable for concealed locations (within walls or under floors) where access for inspection or repair is limited — though manufacturers certify them for such use.

The practical recommendation: Push-fit fittings are excellent for accessible locations, temporary connections, and homeowner-level plumbing tasks. For concealed or permanent installations, compression fittings provide a mechanically more robust connection that many professionals prefer.

Threaded Fittings — Screwing Pipes Together

Threaded fittings use male (external) and female (internal) threads to screw pipes and fittings together. They are common on radiator valves, boiler connections, tap connectors, and wherever a fitting needs to be removable.

PTFE tape or thread sealant is applied to the male thread before assembly to seal the microscopic gaps between the thread surfaces. Without sealant, threaded joints will leak through the thread path.

Threaded fittings are used for connections between different pipe types — for example, connecting a copper pipe (via a compression fitting with a threaded end) to a brass valve with a female thread. They provide a transition between pipe systems and are the standard connection method for valves, taps, and appliances.

Do not confuse thread tightness with seal quality. A threaded joint sealed with PTFE tape should be firm but not forced. Over-tightening can crack brass fittings, strip threads, and distort the fitting, actually making the joint less watertight.

Soldered (Capillary) Fittings — The Professional Standard

Soldered fittings (also called capillary fittings) create a permanent, low-profile joint by melting solder into the gap between a copper pipe and a copper fitting using a blowtorch. The molten solder is drawn into the joint by capillary action, filling the gap completely and forming a strong, watertight bond when it solidifies.

Solder ring fittings contain a pre-loaded ring of solder inside the fitting. When heated, the solder melts and flows automatically, simplifying the process. End-feed fittings require the plumber to feed solder wire into the joint manually as the fitting is heated.

Soldered joints are the strongest, most compact, and least expensive connection for copper pipe. They are the standard method used by professional plumbers for permanent installations.

However, soldering requires a blowtorch, flux, solder, and the skill to apply heat correctly without overheating the joint (which causes the solder to flow out rather than into the joint) or underheating it (which produces a weak, incomplete bond). There is also a fire risk — applying a naked flame near timber, insulation, and plastic components in walls and floors requires fire protection measures.

For homeowners, soldering is a skill worth learning if you plan to do significant plumbing work, but compression and push-fit fittings provide reliable alternatives that avoid the torch entirely. If you are not confident with a blowtorch, use compression or push-fit fittings — there is no shame in this, and the connections are entirely reliable when made correctly.

Fitting Shapes — Couplers, Elbows, Tees, and Reducers

Fittings are available in every shape needed to route pipes through a building.

Straight couplers join two pipes in a straight line. Used for extending a pipe run or repairing a section of pipe.

Elbows (90-degree bends) change the pipe direction by 90 degrees. Available in 15 mm and 22 mm in all fitting types.

45-degree bends change direction by 45 degrees for more gradual turns.

Tee fittings create a branch — one pipe continues straight through while a second pipe branches off at 90 degrees. Used for feeding a new supply point from an existing pipe run.

Reducers connect a larger pipe to a smaller one — for example, a 22 mm main supply down to a 15 mm branch feeding a tap.

Stop ends (caps) seal the end of a pipe permanently.

Each shape is available in compression, push-fit, and soldered versions. Choose the connection method that suits your skill level and the installation requirements, then select the shape that routes the pipe where it needs to go.

Isolation Valves — The Fittings That Let You Turn Off Individual Supplies

An isolation valve (also called a service valve or mini stop valve) is a small inline valve fitted to the supply pipe feeding a tap, toilet cistern, washing machine, or other appliance. It allows you to turn off the water to that specific fixture without shutting off the supply to the entire house.

This is enormously practical. If a tap needs a new cartridge, you turn off the isolation valve under the sink, work on the tap, and turn the valve back on when finished — without interrupting the water supply to the rest of the house. Without an isolation valve, you must turn off the main stopcock to the entire property.

Isolation valves are small compression fittings that install inline in a 15 mm copper or plastic pipe. They are operated with a flat-head screwdriver — a quarter turn opens or closes the valve.

If your existing plumbing does not have isolation valves on taps and toilets, adding them is one of the most useful and straightforward plumbing improvements a homeowner can make. It costs very little, takes minutes per valve, and saves hours of inconvenience every time a fixture needs attention.

Flexible Connectors and Tap Tails — Bridging the Last Gap

Flexible tap connectors (also called flexi hoses or braided hoses) are short lengths of flexible, reinforced hose with threaded fittings at each end. They connect the rigid pipework (terminating at an isolation valve or compression fitting) to the tap body.

Flexible connectors simplify the final connection because they accommodate slight misalignment between the rigid pipe position and the tap inlet position. Without them, the rigid pipe must align precisely with the tap — a requirement that is difficult to achieve in the confined space under a sink.

Length should be sufficient to reach comfortably between the isolation valve and the tap without being excessively long (excess hose kinks and obstructs the space under the sink). Measure the distance and add a modest allowance for the curve of the hose.

Quality matters. Budget flexible connectors with thin braiding and poor-quality fittings can fail — and a burst flexible connector under a sink delivers a continuous flood until the water supply is turned off. Choose connectors with stainless steel braiding, solid brass fittings, and a reputable brand. Replace flexible connectors every five to ten years as a precaution, particularly in locations where a failure would cause significant water damage.

Waste Pipe Fittings — Connecting Drains and Traps

Waste pipe fittings connect the drain outlets from sinks, basins, baths, and showers to the main waste pipe system. They are typically plastic (PVC or ABS) in 32 mm (basin waste) or 40 mm (bath, shower, and kitchen sink waste) sizes.

Push-fit waste fittings use rubber sealing rings and friction grip to connect waste pipes. They are easy to assemble, disassemble, and adjust — ideal for homeowner-level work.

Solvent-weld waste fittings use a chemical solvent (cement) to bond the pipe permanently to the fitting. The joint is stronger and more compact than push-fit but cannot be disassembled without cutting.

Compression waste fittings use the same nut-and-olive principle as supply pipe compression fittings, adapted for larger waste pipe sizes.

Traps (the U-shaped or bottle-shaped fittings beneath every sink, basin, bath, and shower drain) hold a plug of water that prevents sewer gases from entering the room through the drain opening. Every drain must have a trap. Traps are connected using waste pipe fittings and should be accessible for cleaning — hair, soap residue, and debris accumulate in traps and are the most common cause of slow-draining fixtures.

Choosing the Right Fitting for the Job

For copper pipe supply connections where you are comfortable using spanners: Compression fittings. They are the most widely used, most proven, and most versatile option for homeowner-level plumbing.

For copper or plastic pipe where speed and simplicity matter most: Push-fit connectors. They require no tools and no special skill, making them the most accessible option for anyone new to plumbing.

For permanent, concealed installations by a professional: Soldered (capillary) fittings. They are the strongest, most compact, and most cost-effective option for extensive pipework, but require a blowtorch and soldering skill.

For connections to valves, taps, and appliances: Threaded fittings with PTFE tape. These are the standard for connecting components that may need to be removed or replaced.

For drain and waste connections: Push-fit or solvent-weld waste fittings in the appropriate size for the drain.

Pipe Fitting Comparison Table

Common Mistakes People Make

Not cutting the pipe squarely

A pipe that is cut at an angle does not insert fully into the fitting, leaving a gap that prevents proper sealing. Use a pipe cutter (not a hacksaw) for a clean, square cut. If you must use a hacksaw, file the end flat and deburr thoroughly.

Forgetting the pipe insert on plastic pipe

Plastic pipe is softer than copper and will collapse under the compression force of a fitting if it is not supported internally by a pipe insert (stiffener). Every compression and push-fit connection on plastic pipe requires an insert inside the pipe end.

Over-tightening compression fittings

The olive needs to be compressed firmly against the pipe — not crushed. One full turn past hand-tight is the typical guideline, but check the manufacturer's instructions. Over-tightening deforms the olive beyond its sealing shape, damages the thread, and can crack brass fittings.

Wrapping PTFE tape the wrong way on threaded fittings

Wrap clockwise on the male thread (viewed from the end). Wrapping anti-clockwise causes the tape to bunch and unwind as the fitting is screwed together.

Not pushing pipe fully into push-fit fittings

The pipe must reach the internal stop inside the fitting for the O-ring to seal correctly and the grab ring to grip securely. Mark the insertion depth on the pipe before pushing it in, and confirm the mark disappears into the fitting — this verifies full insertion.

Reusing old olives

When disassembling a compression fitting for repair, the old olive has been permanently deformed to the shape of the original connection. Reusing it on a new connection (or even on the same connection after repositioning) often results in a leak. Replace the olive every time a compression joint is remade.

The Honest Limitations

Push-fit fittings are more expensive than compression or soldered alternatives. For a single repair, the difference is trivial. For a full plumbing installation with dozens of fittings, the cost difference adds up significantly.

Compression fittings are bulkier than soldered fittings. In tight spaces — inside wall cavities, between joists, and in confined service voids — the larger profile of compression fittings can make routing pipes more difficult.

No fitting is leak-proof if installed incorrectly. Every fitting type can leak if the pipe is not cut squarely, is not fully inserted, is not properly sealed, or is over-tightened. Correct installation technique is more important than the fitting type.

Push-fit O-rings have a finite lifespan. The rubber O-ring that creates the seal in a push-fit connector can harden and lose elasticity over many years, particularly in hot water systems. Manufacturers certify their fittings for long service lives, but the O-ring is a potential failure point in a way that a compressed olive or a soldered joint is not.

Mixing pipe materials requires care. Connecting copper to plastic requires appropriate fittings and inserts. Connecting copper to galvanised steel requires a dielectric fitting to prevent galvanic corrosion. Using the wrong fitting for a mixed-material connection can cause corrosion, leaks, and premature failure.

Pre-Purchase Checklist

What pipe material and size are you connecting?

Copper 15 mm and 22 mm are the domestic standard for supply. Plastic 15 mm and 22 mm are the alternative. Waste is plastic 32 mm or 40 mm. Match the fitting to the pipe.

What fitting type suits your skill level?

Push-fit for simplicity. Compression for reliable, proven connections. Soldered for professional-grade permanent joints.

What shape fitting do you need?

Straight coupler, elbow, tee, reducer, or stop end — determined by the pipe route and the connection layout.

Do you have pipe inserts for plastic pipe?

Every compression and push-fit connection on plastic pipe requires an insert. Buy them with the fittings.

Do you have spare olives?

Compression olives in 15 mm and 22 mm are inexpensive consumables. Keep a bag of each in your plumbing toolkit for repairs and replacements.

Why Buying Through Amazon Is a Smart Option

Amazon carries pipe fittings in every type, size, and shape — compression, push-fit, threaded, and solvent-weld — along with pipe inserts, olives, PTFE tape, isolation valves, flexible connectors, and waste fittings. Multi-packs of common fittings and olives provide excellent value for homeowners building a plumbing spares kit. Customer feedback provides practical insight into fitting quality and ease of installation. Free returns on most purchases allow you to check compatibility before committing.