A Guide To Pipe Fittings and How To Use Them

If you're doing a plumbing installation or repair, you'll need to buy pipe and pipe fittings. Here's some help figuring out which fittings you need.

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I doubt there’s a DIY plumber out there who hasn’t experienced the frustration making multiple trips to the hardware store to complete a repair. I know I have.

Putting together a network of pipes of different diameters and materials can be like assembling a puzzle. Sometimes you don’t know exactly which fitting to buy until you reach the part of the puzzle where you need it.

Plumbing fittings vary by size, purpose and material. You often must tie together pipes of different materials with transition fittings. The materials in common use today — copper, PVC and CPVC, PEX, ABS, galvanized steel and cast iron — can mostly all be connected to each other with appropriate fittings.

With all the different pipe sizes and materials out there, things can get confusing. Fittings for water lines are different than those for drain and waste lines. It’s no wonder professional plumbers don’t go anywhere without a truck full of fittings. It’s their magic cupboard, letting them complete installations and repairs much more efficiently than amateurs like me.

Water Line Fittings

PEX is quickly becoming the material of choice for water lines. But PVC, CPVC and copper are still in common use, as is galvanized steel outdoors.

Three reasons for PEX’s popularity are its flexibility (it can bend around corners), durability and ease of assembly. You simply push PEX pipes and fittings together rather than gluing (PVC and CPVC), soldering (copper) or screwing them (galvanized steel).

Here are the fittings you’re most likely to need when assembling or repairing water lines:

• Coupler: Joins two lengths of pipe in a straight line. Whenever you cut a pipe during a repair, you’ll need a coupler to put it back together.
• Bend: For changing pipe direction. The most common bend angles are 90 degrees (aka elbows) and 45 degrees. Bends are typically made of the same material as the pipe except for PEX bends, which are brass or hard plastic.
• Tee: Shaped like the letter “T” with two parallel ports and a perpendicular one. It’s used for adding a branch line. When the branch line is a different size than the main one, you can make the connection with a reducing tee.
• Reducing adapter: Another way to join pipes of different diameters. It may be shaped like a bell (common for copper and galvanized pipes) or fit inside the larger pipe (more common for plastic). The first type is a bell adapter, and the second a reducing bushing.
• Union: A type of coupler you can take apart. Its large threaded nut holds together the two halves of the connected pipe. You can use one in place of a coupler in any situation where you temporarily disassemble the pipes.
• Threaded adapter: To join a pipe with a glue or solder slip joint to one with threads, you’ll need a threaded adapter. It can have male or female threads. Threaded adapters join plastic pipes to each other, or copper to itself or to brass.
• Compression fitting: This lets you join plastic or copper pipes without glue or solder. Most feature a ring that fits around the pipe and a nut that tightens onto the fitting, wedging the ring into the gap between the pipe and fitting. Compression fittings allow for easy pipe repair. Most modern faucet and toilet shutoff valves have compression fittings.

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Waste and Drain Fittings

Cast iron was a common material for drain pipes in the first part of the 20th century. They’re usually connected with couplers that feature rubber gaskets surrounded by stainless steel sheathing.

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These days, most drains are made with PVC or ABS plastic. Plastic drain fittings are usually glued, but the ones you might need to remove temporarily, like cleanout plugs, are threaded.

Here are the most common drain fittings. The list doesn’t include couplers and ordinary bends, because they’re similar to the ones used for water pipes and serve the same purposes.

• Long-sweep elbow: Makes a 90-degree bend in a longer arc than an ordinary elbow to allow water to flow more smoothly. It’s used for connecting vertical drain lines to horizontal ones.
• Straight tee: Performs the same function as tees for water lines, but are seldom used for drain lines. They’re mostly for vents, tying horizontal pipes to vertical stacks.
• Sanitary tee: Aka a santee, this has a sweep on its perpendicular port to promote water flow in the direction of the sweep. Use it to connect a horizontal waste line to a vertical one, but not a vertical one to a horizontal one. That’s the job of the next fitting.
• Wye: Shaped like the letter “Y,” a wye does the same job as a sanitary tee, but with less chance of backflow. This is the fitting you need to connect the vertical drain from your sink or toilet to the sewer. You can also use it to connect a horizontal waste pipe to a vertical one.
• Double wye: As you might expect, this has two inlet ports instead of just one. It’s commonly used for connecting a double-basin sink to a single P-trap.

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Transition Fittings

Whether you’re connecting PVC or CPVC pipes to copper, cast iron pipes to ABS or galvanized pipes to copper, you’ll need a transition fitting. In some cases, you can do it by taking two threaded adapters of different materials and screwing them together. But it’s often easier to use an adapter specifically made to couple them, assuming you can find one.

• Plastic-to-copper slip adapter: This fitting has male copper threads on one end and a PVC or CPVC slip joint on the other. After soldering a female thread adapter to the copper pipe, you screw in the adapter and glue the plastic pipe to the slip joint.
• Dielectric union: Used for mating copper or brass to galvanized steel, its insulating washer keeps the pipes electrostatically separated to prevent corrosion. Dielectric unions are commonly used when installing water heaters.
• Cast iron to plastic coupling: These are widely known as Fernco couplings after the company that makes most of them. They consist of a rubber cylinder surrounded by a stainless steel sheath and two or more threaded pipe clamps tightened with a screwdriver.

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Pipefitters please! Residential black iron/galvi gas fitting "rules"?

I have yet to see a basic "set of rules" on residential 1/2" to 1 1/2" gas piping and was hoping to get some insight from the people TRAINED in it. I know, i know....everyone has a way that works.... I just want to know what the "trained" way is or a list of things anyone could walk on a gas job and look at to tell if its at least somewhat correct. Things you would fire someone over if they couldn't at least follow these "basics".

All sizes discussed are 1/2" to 1 1/2" black iron or galvi pipe..
Are these generalizations fairly correct or am I way off? Just looking for knowledge here....

1. Amount of thread inserted into fitting is roughly the diameter of the fitting. IE: A 3/4" pipe will have roughly 3/4" of threads threaded into the fitting. In other words, you could measure fitting to fitting, and add 1 1/2" total to get correct pipe length.

2. Cutting threads- More oil the better, slow steady cutting movements to avoid tear outs.

3. Threads- sizing and amount

Thread cut size- It seems like well-cut threads will hand thread DRY roughly 3-4 full turns before stopping by hand. With teflon tape or dope, they will thread in another 3 or so full turns with a proper sized pipe wrench, for a total of 6-7 fully threaded threads.

Thread counts- When cutting in threads, roughly 9 full depth threads should be cut (with a couple partials on top of that). Once fully doped/taped up, the pipe will thread a full 6-7 rotations. This will leave 2-3 full depth threads visible after all assembled, if properly tightened. If there are no visible threads, the pipe was tightened too tight (deeply buried) or threads were cut too loose. If more than 3 full depth threads are visible, the piece was cut with too many threads (more than 9 or 10 full depth threads) or the joint is too tight.

4. Teflon tape-

Type- Special gas teflon tape should be used. The yellow gas tape is most common and easily identifiable. There are other brands, we won't get into a pissing match over brands.

Amount- If using the yellow gas tape, roughly 3-4 full wraps on all threads is most often used for adequate seal. More or less can be used if threads are a little "loose" or "tight".

Where- Do not tape or dope the first thread, some people say first two threads, to avoid contaminating inside of the lines.

Question- Are you running those 3-4 wraps of tape all the way up a larger pipe, like a 1" pipe? IE: Do you wrap ALL the threads 3-4 full wraps or do you just start two threads up and wrap in a circle(IE: bare threads above and below circle of tape or tape everything?)



5. Dope-

Pipe dope can and often is used on top of teflon tape. There are many brands that people like and use. Rectorseal number 5 appears to be the most common and widely used, although many others can be used.

Question- Outside of personal preference, is there a "rule" of when to use a soft set, hard set, or never set dope? IE: Is there a rule that says "if you are running pipe between floors of a house that will have some bounce and rattle, you SHOULD use soft flex...." or "If in earthquake area you should use soft set but if you install in sub-zero areas you should use hard seal"? Any hard rules like that?

6. Pressure testing- Requirements vary, but often 10-15psi is used to pressurize the pipes and let them sit for various amounts of time. Often, not less than one hour. Heating or cooling pipes can affect this number so be aware if your attic got 30 degrees cooler since starting the test.

A manometer can also be used to test for leaks but I am too dumb to understand how this works, although I own one. Feel free to educate me if you feel so inclined...it will be life-long knowledge if you do so.

7. All valves/appliances should be capped off before testing or the valves can be damaged.

8. Most gas pressure is regulated before or at the meter in residential situations, often with pressures of less than 1 or 2psi.

9. Tightening gas pipes with the PROPER monkey wrench requires a good amount of force and will snug up pretty damn tight when done right....using a grossly oversized or undersized pipe wrench can result in grossly under or over torqued pipes, resulting in cracks or leaks.

10. Once a pipe is loosened any amount (even by accident when installing another pipe) the pipe should be fully removed, re-taped and doped, and re-installed. Does slow setting or soft setting pipe dope give a little more wiggle room with this? if you accidentally loosened a one-day old installed pipe that was set with rectorseal 5, would you just re-tighten or would you remove and reinstall? Why do they even make hard setting compounds?

11. Drip legs and sediment traps vary by code, but basically go before appliance connections or at appliance connections to trap debri, oil, and moisture before reaching the appliance.

12. Pipe Origin- China pipe is often more difficult to thread and has poorer fittings than usa made, although usa made is getting hard to find.

Are there brands you guys like for fittings and pipe that could be used in residential?

13. Galvi vs. black steel- Just depends on location and code. Many old-school guys say galvi can flake and clog gas orifices but other say the new cheap black steel will rust and do the same. Other say both are equal, other say "I only use this and the other is wrong..." Both are used in many places, but it seems like something around lots of water or the ocean would require galvi.


Feel free to tear me a apart or educate me...looking to learn or verify what has been learned here... Please don't take offence to this, but this is not a question for someone who has "installed a gas heater or two" or who has hooked up their own range

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