Houses typically have three different kinds of lines:

Supply lines: these pipes are under an inch in diameter can best be viewed going in and out of the top of the water heater, under the kitchen or bathroom sink, or under the toilet tank.

Waste lines: these pipes are 1½"- 4" in diameter and are located under the house.

Gas lines: these pipes are easily mistaken for water pipes as they often are the same size and of the same or similar material. A gas pipe also runs to the water heater, but to the underside not the top. Gas pipes are often black iron pipes.

Hot and cold water lines often run parallel to each other about one foot apart, whereas gas lines usually run by themselves. Water lines are usually fit snug against the floor joists and are secured tightly, while gas lines (which carry much less pressure) tend to be less snug and less well-secured.

There are also vents that remove exhaust gases from gas appliances. These are not easily mistaken for water pipes as they are 2½" to 4” in diameter, are made of thin metal and do not look like they would hold water.

Determine if the supply lines are copper, PVC or galvanized. The best place to determine if the supply lines are copper, PVC or galvanized steel is at the top of the water heater.

Under every plumbing fixture in the house, there is usually a water shut-off valve for both the cold and hot water (toilets only have cold water) pipes, although there is not always enough play to slide it forward.

When sweating a copper joint, use a metal flame shield in tight places to protect surrounding areas from catching fire. Use lead-free solder with appropriate flux. Be sure to clean pipe with steel brush inside of female connector and outside of male with sand paper before soldering.

Wear safety glasses, a hat and gloves when cutting pipe or soldering a joint, especially if making a repair where you must reach over your head.

Clean all types of pipe at joints before making connections; bad joints are the main cause of leaks. With PVC and CPVC pipe, use primer before applying solvent cement.

Always have adequate ventilation when using solvents to prevent buildup of fumes

Local building codes in place in most areas require compliance in all plumbing. Be sure before starting your work that you will comply with any local codes.

Copper Pipe

Rigid copper pipe is good for new installation. Soft or flexible copper pipe is good for repair work since it can bend around obstacles without multiple cuts and joints.

Type K is heaviest, used in municipal, commercial, residential and underground installation; Type L is medium weight and is the most commonly used in residential water lines; Type M is hard and thin.

Recommended for light domestic water lines and not permitted in some city codes or for underground use.

Common sizes are 3/8”, ½", 3/4” and 1".

Refrigeration tubing has moisture removed and ends sealed for refrigerants. Often used in heater connections but may corrode. For heater connections, use flexible brass or aluminum.

Larger sizes also used for DWV (drain-waste-vent) applications.

PVC Pipe

PVC stands for Polyvinyl Chloride.

Used for carrying cold water and irrigation, as electrical conduit and for DWV (drain-waste-vent) projects.

Rated by thickness and strength. Common ratings (thickest to thinnest) are Schedule 40 (most common), Class 315, Class 200 and Class 125 (generally used for irrigation).

Common sizes from 1/2” to 6” but available in larger sizes. White in color.

CPVC Pipe

CPVC stands for Chlorinated Polyvinyl Chloride.

Used for both hot and cold water supply or chemical distribution systems.

Good for temperatures at 200° F in pressure systems and non-pressure systems.

Requires special solvent cement that is different from cement used for other types of plastic solvents. Most solvents will indicate this on the can.

ABS Pipe

Means Acrylonitrile Butadiene Styrene.

Made from a thermoplastic resin. Lightweight and easier to use than metal pipe.

Commonly used for DWV (drain-waste-vent) applications or for underground electrical conduits.

Available as either solid-wall or cellular-core construction

Black Poly Pipe

Used for carrying low-pressure cold water. Common applications include golf course sprinklers and underground conduits or to carry corrosive liquids and gases.

Good chemical and crush resistance.

Lightweight enough to cut with an ordinary knife or a fine-toothed hacksaw blade.

PEX Pipe

PEX stands for crosslinked polyethylene.

Chief advantage is its flexibility and strength. It can make turns around corners without couplings.

In a PEX plumbing system, a separate line is run from the main water supply to each fixture in a setup much like a circuit breaker box.

Used for carrying hot and cold water.

Excellent chemical resistance to acids and alkalis, but do not use for fuel oil, gasoline or kerosene systems.

Do not weld with solvents. Join with heat fusion, flare, crimp ring or compression fittings.

Galvanized Pipe

Has zinc coating that prevents rust if not scratched.

Use primarily for carrying water or waste. Do not use for gas or steam.

Common water sizes are 3/8”, 1/2”, 3/4” and 1”. Common waste sizes are 1-1/2”, 2” and 3”.

Often sold in pre-threaded standard lengths or can be custom threaded.

Use only with similar galvanized pipe fittings, not with black pipe fittings.

Measure using the I.D. (inside diameter).

Black Iron Pipe

Not treated for rust resistance.

Used for carrying steam or gas.

Used only with black iron pipe fittings, not galvanized fittings.

Measured using the I.D. (inside diameter).

Cast Iron drain pipe

Cast iron was used for years as the primary pipe for sewerage drains under slab-type houses and in elevated-foundation residences. This pipe is seldom used today, but when repairing older homes you may find this pipe. Adapters are available to connect to the common pipes of today.

Water Supply Tube

Used to connect a water supply pipes to a faucet fixture, toilet or appliances. Several types available.

Plastic type is flexible and inexpensive but not designed for exposed connections.

Ribbed chrome type bends easily without kinking.

Braided type features pre-attached connector nuts at both ends and can be flexed to fit.

Chrome-plated copper or brass tubes are more rigid than other types and are good for exposed applications.

The most common size is 3/8", with lengths ranging from 6" to 72".

Vinyl Tubing

Economical and used in a variety of applications.

Usually joined with pressure fittings and clamps.

Traps

Installed under sinks and tubs to route wastewater to the drain. Primary purpose is to prevent sewerage gases from entering the structure.

Bridges the gap between the sink tailpiece and the drain line.

The bend in the trap uses gravity to hold water and prevent sewer gas from seeping into the house.

Attach using slip nuts.

Three configurations include: P trap, S trap and J bend.

Most common sizes are 1-1/4” and 1-1/2”.

Also available is a trap with flexible tubes that help in connecting misalignments of the tailpiece and the drain line.

Available in plastic and chrome-plated brass.

Tub Drain

Uses an overflow opening to control draining in a tub.

The spring type consists of an assembly controlled by a lever that moves a pop-up plug up and down. It is easiest to install, especially in retrofits.

The weight type consists of an assembly that controls a weight that lifts up or down out of the drain hole. It is also controlled by a lever.

Pop-Up Drain

Also known as a P.O. drain.

Controls the mechanism in a lavatory sink with a plug that can open or close the drain.

Reference:

The North American Retail Hardware Association