This post is another in a series of helpful tutorials for our friends in Nassau County and NYC.  Replacing a sink P trap is a commonly needed repair whether you live in a small town like East Williston in Nassau County, or any other neighborhood across the country. Second to using a plunger, the next easiest thing to do in a plumbing installation is replacing a sink P trap. This plumbing part is the U-shaped assembly installed underneath a sink. It is called P trap because it looks like a face-down letter P.

P trap

The Belly of a P trap has a water barrier and catches debris

Every plumbing trap has a U shape because it has to hold water inside the curved portion of the assembly. This “belly” in every trap acts as a water barrier to prevent sewer gases form escaping into your living environment. When you wash anything down the sink, waste materials pass that curved shape followed by clean water behind it. That clean water remains in the pipe to prevent toxic gas or odor from entering your house. There should be a P trap connected to every drain except a toilet because it already has one built into the bowl.

The components of a sink P trap

A new P trap assembly usually comes with a tailpiece, a trap adapter to connect the curved pipe to tailpiece, u-shaped pipe with clean-out access, and a trap arm. Starting from the top, everything should be connected to the sink drain in that particular order. Every part is secured to another by a slip nut, which looks like any regular nut, only larger in diameter. Depending on the models and brands, the assembly can be made entirely of plastic such as PVS and ABS or even metal as long as it is rust-resistant.

sink P trap

Always have a bucket to catch old and dirty water before taking apart your plumbing

Replacing a P trap requires minimum, if any specialty tools at all. You can even loosen and tighten slip nuts with your bare hands in some instances. Remember to never use a lot of force, with or without tools. If you do need tools, some basic 14″ plumbing wrenches are probably best to use. You will also need a hacksaw, or 2″ tubing cutter. If your fittings are chrome, wrap a cloth around them to prevent the wrenches from scarring their finish.

To prevent leaking, you can wrap the threaded portion of each part with Teflon plumbers tape, or pipe joint compound. Since the curved portion of the assembly contains water (it may be filled with gunky stuff), you are advised to put a bucket with a rag inside, underneath the pipe before removing the assembly. If the old sink P trap has a clean out access, drain the water first by opening the plug.

Here’s Your 6 Step Sink P Trap Replacement Plan:

1. Remove all parts of the old assembly by loosening the slip nuts that hold them together. You only need to remove two really; the one that connects to the tailpiece and another on the trap arm. Assuming you want to discard the old assembly entirely, there is no need to loosen the nuts on the curved portion anyway. Loosen the slip nuts using your hands. If you find them too tight, use a pipe wrench or tongue-and-groove pliers instead. Start with the tailpiece, and the pipe should come right off. If it doesn’t, give a little wiggle while pulling it downward. Repeat the process with the slip nuts on the trap arm and pull it out of the drain pipe in the wall.

2. Clean the threaded parts of the wall pipe and tailpiece connection for the new assembly. If there is a lot of dirt or sediment, use a wire brush. Better to be safe, than have a leak afterwards.

3. Measure the length of the new tailpiece and trap arm you need. Also check if the new pipes have the right diameter. If you have to custom cut the pieces use a 2″ tubing cutter or a hacksaw. A tubing cutter will give you a cleaner and more precise cut.

4. In most cases, you can assemble the tailpiece, the trap itself, and trap arm before you connect them to the sink and drain pipe. Remember the order of installation mentioned above. Never over-tighten or use brute force, many sink drain pieces are relatively fragile.

5. You may need to cut the tailpiece and trap arm to length afterward. The point is to make sure that the sink P trap assembly is properly angled. A misalignment can lead to an annoying leak after the fact. There should 90-degree bend between the tail piece and trap arm.

6. Connect the new tailpiece to the bottom of the sink and trap arm to wall drain pipe. If needs be, apply Teflon tape of pipe joint compound to the threaded parts for better sealing. Tighten all the slip nuts, and you are done. A tip: If you pipe is properly aligned they can be hand tightened almost entirely. Use your wrenches for only one final 1/4 or 1/2 a turn.

Know the limits of your plumbing skill-set

old sink drain line

Some sink P trap replacements are more difficult than others

Not all sink P trap replacements are as easy as others. Older, mixed material, multi-component sink drains can pose challenges. Older, thinner, sink drain components tend to bend or break. When brass or steel fittings are involved, they may have become frozen in place over time. In some cases, the pipe diameters may not even be all the same. That said, consider your quick plumbing project carefully before it becomes your “weekend event”.

Check your work before you “close up shop”

Don’t forget to check for leaks. Run water from the sink and see if you have drops of water underneath the trap. Thanks to the design of a P trap, toxic gas and odor from the septic tank or sewer cannot escape into your house. However, the shape can also create a little bit of difficulty for slightly larger material to flow into the drain. Water that contains a lot of mineral may leave debris inside the trap too.

Choose a trap with clean out access so you can get rid of such debris without removing the entire assembly. Many sink traps, such as the one pictured above, has a clean-out plug right on the bottom. Just always remember to place a bucket underneath the catch the slimy stuff about the fall out of your trap. If you’d like to learn more about your drain system components read about 13 Drain Hardware Components.

About Your Balkan Drain Team

Your Balkan Drain Team is really your Drain Dream Team. We provide expert advice via email or phone, and via our ongoing series of helpful household plumbing tutorials. When you cannot figure it out yourself, depend on us for expert and timely drain, sewer, and water line service. Contact Balkan virtually any time, and any day of the week to receive on-point plumbing service.

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