Everything You Need to Know About Working With Plastic Pipe

Lead Image
What You'll Need
Pipes, tubes, fittings
Miter box
PTFE plumber's tape
Channel-locking pliers
Silicone rubber sealant (RTV) or plumber's putty
Solvent cement
Fine-tooth saw
Clean cloths
Plastic pipe cutter
Flaring tool
Hand cleaner

Plastic piping and do-it-yourself projects go together like wood and a saw. Plastic pipe is not only easy to cut, but it is also easy to join to with many fittings. It is widely accepted by plumbing codes. This article will explains how to meet the plastics, weld the solvents, manipulate mechanical couplings, and install plastic pipes.

Meet the Plastics

Thermoplastic plastic is categorized two ways, which are pipe sizes and tubing sizes. Both are sized according to the interior diameter. Pipes are listed by iron-pipe sizes. Tubes are organized by copper-tube sizes. Pipes and tubes should not be interchanged. A wide selection of plastic pipes are available. Table A shows the types of plastic plumbing available and explains the purpose of each one.

Local plumbing codes may become outdated by technological advances in plastic plumbing. Consult your local building officials before purchasing your materials.

DWV stands for the drain-waste-vent system. It is used to carry waste away from your home and to vent the system. Sewer pipes carry household waste below ground to a public sewer or private disposal system. Drainage pipes are also below, but they are thinner and less expensive. Drainage pipes are commonly used for non-septic water.

They may be used in tandem or individually to build corrosion-free, non-electrolytic household water supply systems. Because plastic pipe is non-conducting, it cannot be used for electrical grounding.

PVC pressure pipes should only be used to transport cold water outdoors. It is ideal for lawn-watering and irrigation systems. PE pipe serves a similar purpose, but this type of pipe is flexible and cannot be solvent welded. PE is especially useful for deep-wells.

Welding With Solvents

plastic pipes supported near the ceiling

Solvent welding process is used to join plastic pipes in order to prevent leaks. Use this 2-step method, which employs cleaner, primer and solvent. Processes for ABS and styrene, however, use a 1-step method.

Inspect the pipe end and fitting socket for cracks, gouges, dirt, and abrasions. If the pipe end is damaged, cut it to expose good material and discard the damaged fitting.

Purchase pipes and fittings manufactured by the same company. If you cannot match the manufacturer, test-fit the pipes. The pipe should not only enter the fitting, but it should also meet resistance part-way in. Held upside down, the pipe should not fall off.

Cutting Pipes

Cut the pipe squarely to the proper length with a fine-tooth saw or plastic pipe cutter. For large amounts of cutting, get a tubing cutter with a special wheel for use on rigid plastics. Using a knife, remove any burrs and slightly chamfer the outer end of the pipe. Do not use sandpaper on plastic pipes. It may remove too much material for successful joining.


Using a quality cleaner and primer, clean the pipe end and fitting socket. Apply the chemicals with either a brush or clean cloth to remove grease, oil, and dirt. The primer also prepares the plastic mating surfaces for the solvent cement. The pipe should be dry before applying cement.

Solvent Welding

Apply a coat of an ASTM-rated solvent cement that is suitable for the type of pipe and fitting you are using. You must use the right type of solvent cement. Table B shows the various cements and the kinds of plastic to which they are suited.

Liberally apply cement to the pipe end. Then apply it sparingly to the fitting socket; do not leave any bare spots. Apply several coats of cement to the chemical-resistant PVC and CPVC pressurized piping. To solvent welding chemicals, use a brush that's at least one-third to one-half the pipe's diameter.

Immediately join the pipe and fitting full-depth with a slight twist to bring it into correct alignment. The twist breaks insertion lines in the solvent cement. Hold the fitting until the solvent cement forms a secure bond.

A fillet of cement around the fitting indicates that you have applied a sufficient amount of solvent cement to ensure a leak-free joint. With PVC and CPVC, do not wipe off the fillet. The one-step solvent-welding method for ABS and styrene calls simply wiping excess cement from the fitting. The joint should be ready for use in an hour.

Safety Precaution

Avoid prolonged exposure to vapors by working in a well-ventilated area and capping the cans after each use. Keep solvents and cleaners away from open flames. Read and follow the safety warning on the product labels. Use hand cleaner to remove cement from your hands.

Correcting Errors

blue pvc pipling

Solvent welding is normally a 1-way process. You can install the fitting, but you cannot remove it. When you accidentally put the wrong fitting on a pipe, you must cut it out and replace it with the correct fitting.

Mechanical Couplings

Come fittings are made for joining pipes and tubes that cannot be solvent welded.

PE Pipe

Simple barb-type plastic or metal fittings are used with flexible PE pipe. Make the connection simply by sliding a correctly sized worm-drive clamp over the pipe end. Push the pipe all the way onto the barbed fitting. Position the clamp at .25-inches from the end of the pipe and tighten it.

Take care not to tightly bend the flexible tubes. It can kink the tube and either diminish or completely close the water flow.

PB Tubing

O-rings are used to form the joints. Each system uses its own coupling. They are not interchangeable in most cases. Follow the label instructions.

Flaring Plastic

Both CPVC and PB tubing can be joined to metal piping, as well as to each other, with flare or compression couplings and adapters. Flaring is performed with a flaring tool.

To prevent cracking a CPVC tube during flaring, cut the end squarely and smoothly with a pipe or tubing cutter, then soak the rigid tube's end in boiling water immediately prior to flaring.

Slip Jam Nut Couplings

Tubular drainage pipes are joined by slip jam nut couplings. To form a slip jam nut couplings, install the nut facing its threads. Then install the slip washer with the flat side facing the nut. Adjust the length and direction of the tubes, thread the nut, and tighten it. Most plastic tubular couplings will seal by hand. You may want to give them an extra quarter-turn with a channel-locking pliers.

Transition Unions

Transition fittings are used to adapt plastic water supply tubing to threaded metal parts, such as at water heaters and bathtub or shower valves. Transition unions allow leak-free thermal movements between metal and plastic. Use a male-threads adapter for non-pressurized connections.

Mechanical couplings for PB water supply tubing work with copper tubing because they are the same size. They allow you to joint plastic to copper without sweat-soldering; they make effective transition unions.

Flexible Fittings

Vinyl with clamps comprise comprise these parts. A flexible fitting can be shoehorned into place, despite he unmovable nature of the pipes over which it fits.


Mount the plastic pipes so that they can expand and contract without damage. Large DWV pipes are hung with plumber's tape. They are spaced at a maximum of 48-inches apart.

Smaller water supply tubes are attached to the framing with tubing hangers which permit back-and-forth movement. Place hangers 32-inches apart and be certain not to bind rigid pipes at the ends. Leave .25-feet for every 10-feet of pipe.

Protect against nails with pre-punched and nailed-on steel straps from your dealer. The straps brace notches in the framing which are used for piping. Install air chambers or hammer arresters at every fixture and appliance, except toilets.

Joining to an Existing Drain

Slip couplings are excellent when the project mandates that you must connect new drains to old drains. Draw lines indicating where to cut and saw the length of pipe between the marks. Use a slip coupling which is designed without a shoulder. Position the new fitting onto the old pipe. The joints for solvent welding will have pipe stubs on both sides.

Dope the pipe ends all around with a heavy coating of solvent cement. Immediately slide the slip coupling into place. Twist it slightly as you put it in place. Hold the alignment for 10 seconds before moving to the other end of the fitting.

Direct Burial

When plastic sewer and drain pipes are buried, follow a few common-sense rules. Lay the pipes on the trench bottom. Dig depressions for the couplings so that lengths of pipe are fully bedded. The backfill around the pipes should be free from rocks. Packed sand is a good initial backfill. Once the pipes are well covered, use ordinary backfill.

Information in this article has been furnished by the National Retail Hardware Association (NRHA) and associated contributors.