Omar Khalid
Replacing the plastic pipe under your sink is a common plumbing issue that can be fixed with just a few tools and a trip to your local hardware store. The curved pieces of drain pipe underneath your sink are commonly referred to as P-traps, and they can often leak, become corroded, or get clogged with accumulated soap and grease over time. To replace the plastic pipe under your sink, you will need to remove the old drain assembly, construct a new trap, and install the new strainer assembly.
| Characteristics | Values |
|---|---|
| Tools required | Slip-joint pliers, hacksaw, utility knife, bucket or bag, tape measure |
| Pipe material | PVC, polypropylene (white or black), ABS (black), brass (chrome-plated or natural), metal |
| Pipe diameter | 1-1/4 inch (standard bathroom sink), 1-1/2 inch (standard kitchen sink) |
| Pipe cement | Purple primer for PVC |
| Pipe washers | Rubber, cardboard, cone |
| Pipe coupler | Rubber |
| Pipe fittings | Compression |
| Pipe joints | Ground joint, Slip joint |
| Pipe assembly | Side outlet, center outlet |
| Pipe parts | Tailpieces, trap arm extender, dishwasher wye, disposer kit |
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What You'll Learn
Identify the type of plastic pipe
Identifying the type of plastic pipe under your sink requires some detective work, as most homes are built with multiple pipe materials. Over time, with remodelling and repairs, newer types of pipes may have been added. So, if your home is older than 40 years, you likely have four or more different pipe materials.
The newer pipes are usually the most visible, under the sinks and at the water heater. However, different pipes may be hidden from view in the walls, under the floor, or in the attic.
Polyvinyl-chloride (PVC): PVC is a white plastic pipe often used for water service piping to a home and for sprinkler system piping. It is not approved for use as an indoor water pipe or with hot water. However, it is commonly used for drain piping. PVC pipes will have the letters "PVC" stamped on them.
Polybutylene (PB): Polybutylene is a flexible plastic pipe that is usually grey but can also be blue or black. It has copper crimped rings securing the pipe at connections and is typically stamped with the marking "PB2110". Polybutylene was used in residential water supply piping from 1978 to 1995 but is no longer manufactured.
Cross-linked polyethylene (PEX): PEX is the newest type of pipe for residential use and is approved in many regions. It is easy to install due to its flexibility and use of compression fittings. However, more permanent connections require a special crimping tool.
To identify the type of plastic pipe under your sink, start by looking for any visible markings or stamps on the pipe, such as "PVC" or "PB2110". Also, take note of the colour and any distinctive features, such as copper crimped rings. If the pipe is hidden or difficult to access, you may need to consult a professional plumber or refer to the building plans for your home.
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Measure and cut new pipe
When replacing the plastic pipe under your sink, the first step is to measure the length of the pipe that needs to be replaced. Uncouple any straight pipes that require replacement and measure their length. It is advisable to mark and cut the new pipes a bit longer than needed, as you can always cut them again if necessary, but cutting them too short will require an extra trip to the hardware store.
Once you have the measurements, you can cut the new straight PVC pipes accordingly. Use a small hacksaw to carefully cut the pipes to size. After cutting, use a utility knife to trim any burrs from the ends of the pipe.
If you are constructing a new trap, you can use the old pipe as a model. Assemble the trap according to the package directions.
Remember to use new washers and compression nuts, as reusing old ones can lead to leaks.
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Assemble the trap
When assembling the trap, it is important to use the same type of trap that was removed. Traps are made from polypropylene (white or black), ABS (black), PVC (white) or brass (either chrome-plated or natural colour). The trap should be either 1-1/4 inch (standard bathroom sink) or 1-1/2 inch (standard kitchen sink) in inside diameter sizes.
To assemble the trap, first, attach the trap bend to the trap arm, using slip nuts and washers. The beveled side of the washers should face the trap bend. Tighten all the nuts with a pair of slip-joint pliers. Be careful not to overtighten and crack the slip nuts.
If you are using PVC pipes, you can cement the adapter to a 4-inch piece of straight pipe and then join the plastic pipe to the old metal pipe using a rubber coupler.
Once the trap is assembled, it is important to test for leaks. Turn the water back on by twisting the handle on the shut-off valve. To test the trap, turn the sink faucet on all the way and allow the water to run down the drain. Watch the slip-nut connections for leaks. If you see any, use the pliers to tighten the slip nut. Make small movements to avoid overtightening. Continue to tighten until the leak stops.
Do not reuse old washers or compression nuts as they often leak badly after being removed and replaced.
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Attach the trap bend
Attaching the trap bend is a crucial step in installing a new P-trap, which is the curved portion of piping under the sink that prevents sewer gases from entering your home and stops items from falling down the drain. To attach the trap bend, follow these steps:
First, ensure you have the correct washers and slip nuts for your trap. Use rubber and cardboard washers, with the beveled side facing the trap bend. Position the washers between the underside of the sink and the top of the locknut. Then, attach the trap bend to the trap arm, tightening all the nuts with slip-joint pliers. Be careful not to overtighten, as this can crack the slip nuts.
If you are using PVC pipes, you will also need to use the correct cement for the plastic. Cement a 4-inch piece of straight pipe to the adapter, and then join the plastic pipe to the old metal pipe using a rubber coupler. If your old pipe is made of metal, you may need to use a new pipe as a model to ensure the correct measurements.
Once the trap bend is secure, you can test your work by turning the water back on and observing the slip-nut connections for any leaks. If you notice any leaks, use the slip-joint pliers to tighten the slip nut gradually, being careful not to overtighten.
By carefully following these steps, you can successfully attach the trap bend and complete your P-trap installation.
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Test for leaks
Once you've replaced the plastic pipe under your sink, it's important to test for leaks to ensure your repair work is successful. Here's a detailed guide on how to do this:
- Turn the Water Back On: Start by twisting the handle on the shut-off valve to restore water flow to the sink.
- Run Water: Turn on the sink faucet fully and let water run down the drain. This step helps identify any potential leaks.
- Inspect Slip-Nut Connections: Watch the slip-nut connections carefully for any signs of leaking. Slip nuts are the round fasteners that connect different sections of pipes.
- Tighten Slip Nuts if Necessary: If you notice any leaks, use a pair of slip-joint pliers to carefully tighten the slip nuts. Make small adjustments to avoid overtightening, which can crack the nuts. Continue tightening until the leak stops.
- Check for Drips Underneath the Sink: After running water for a while, turn off the faucet. Check underneath the sink for any signs of water dripping or accumulating. Dry conditions indicate a successful repair.
- Address Persistent Leaks: If leaks persist, you may need to explore other solutions. This could include replacing washers, gaskets, or the entire drain assembly, depending on the specific issue.
It is important to address leaks promptly to prevent water damage to the area under the sink and to avoid creating conditions for unhealthy mold growth. If you're unable to fix the leak, consider seeking assistance from a professional plumber.
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Frequently asked questions
First, use pliers to loosen and unscrew the slip nuts. Drop the pipe assembly down and remove it. Then, use the old pipe as a model to construct your new trap. Uncouple any straight pipes that need replacing, measure their length, and mark new straight pipes before cutting them with a hacksaw. Assemble the trap, slide each compression nut into place, and hand-tighten all the joints. Slip the assembly into place and hand-tighten the nuts onto the nearby pipes. Finally, use slip-joint pliers to turn each nut a half-turn.
You will need a bucket or bag, slip-joint pliers, a small hacksaw, a utility knife, and replacement parts such as washers, nuts, and pipes. You can buy kits for side or center outlet assemblies, but you may also need long tailpieces, a trap arm extender, a dishwasher wye, or a disposer kit.
When in doubt, mark and cut pipes a bit long as you can always cut them again if needed. Do not reuse old washers or compression nuts as they may leak. If you are not replacing the entire PVC drain system, make sure you purchase replacement parts that will match your system.
