An Elbow Trap, also called a J-Bend, is a U- or J-shaped bend in the plumbing under a sink. Its purpose is to create a natural spot to form a clog, so when a clog does form, it is in a convenient location to clean out. If the elbow trap were not there, the clog might occur farther down the piping, behind a wall or under a floor, where it would be harder to get to.

Elbow traps also catch wedding rings, contact lenses, plastic caps, and other small things you might accidentally drop into the sink. Chances are the lost item won't make it past the elbow trap if you shut off the water right away, and can be retrieved by removing the trap.

How to change an elbow trap

This How To is intended for someone who has never done any plumbing before. These instructions will focus on chrome or brass pipe, not plastic or sweat soldered copper.

You should know what the parts of the plumbing are called before we start. First is the tail piece which is in the bottom of the sink. This is the part that is connected to the drain, and it is threaded. Next, you may or may not have a slip joint extension tube. This is a 6 inch or 12 inch tube used to connect the tail piece to the elbow trap (also called a J-Bend), if the elbow trap isn't directly connected to the tail piece. Next is the elbow trap, and finally the connection to the rest of the plumbing.

First, figure out what kind of piping you have installed under your sink. There are three common types in residential installations, the S-Trap floor connection, P-Trap wall connection, and the Cast Elbow wall connection. They come in 1-1/4 inch and 1-1/2 inch outer diameter sizes.

How to tell the difference:

  • S-Trap: Comes down out of the sink, back up to form the elbow trap, and then back down directly into the floor. In this case, the nut connecting the J-Bend to the floor connection will be attached to the floor connection, not the J-Bend.
  • P-Trap: Comes down out of the sink, back up to form the elbow trap, and then horizontally into the wall. In this case, the nut connecting the J-Bend to the wall connection will be attached to the wall connection, not the J-Bend.
  • Cast Elbow: Very similar to the P-Trap, but the connection to the wall is made with a thick pipe rather than thin chrome or brass pipe, like the rest of the connection to the sink is made of. In this case, the nut connecting the J-Bend to the cast pipe will be attached to the J-Bend, not the wall connection. This means the nut is upside down from what you would expect, and will turn clockwise as seen from the top to loosen it.

Now that you know the kind and diameter of piping you have installed, get your materials together. You should be able to find everything you need in the plumbing section of any well-stocked hardware store.

Materials needed:

  • Wrench: big enough to fit over the nuts. If you have 1-1/2 inch pipe, you probably don't have a big enough wrench. Go buy a new one. Don't get anything that looks like a nifty gimmick, it won't work as well as a good old fashioned adjustable wrench. Don't use a pipe wrench, or you'll strip your nuts.
  • Bucket: small enough to fit under the J-Bend but big enough to hold at least a gallon of water. If your sink is full and won't drain, and you can't unclog it, bail it out before starting. When you loosen the pipes, any water that is trapped in the pipe will drain into this bucket.
  • Teflon thread tape: This will seal the threads to prevent leaks. It is very important to use plenty of it, four or five wraps around the threads, because residential pipe is thin and delicate, and will break if you try to tighten it too hard. Always wrap in the direction the nut will be threaded on, so that the action of threading on the nut will not unwind the tape.
  • Rubber gaskets: Sometimes called washers in the hardware store, but they're actually gaskets. The important thing is you want rubber rings, not metal rings. Get one for every joint in the plumbing under the sink, and one spare just in case. They're cheap.
  • Nuts: These will hold the pipe together. Do not tighten them too much or you'll break the pipe, they're thin and fragile. The new J-Bend you buy should come with nuts, but get a spare just in case.
  • J-Bend: of appropriate diameter and style as outlined above. Should come with nuts. It is important not to confuse the Cast Elbow connection with the S- or P-Trap connection, because the Cast Elbow connection has a nut attached to the J-Bend.
  • Slip joint extension tube: If you think you need to replace it, too. Be sure to get the correct length, they come in 6 inch and 12 inch lengths and can be shortened with a hacksaw if necessary. You will notice the end that fits into the J-Bend is plain, no threads or flange. A plastic ring that comes with either the extension tube or the J-Bend will seal the connection.
  • Hacksaw: If you need to shorten your slip joint extension tube. Be sure to cut off the plain end, and leave at least a couple inches for the slip joint to extend down into the top of the J-Bend. It's designed this way so you don't have to be take perfect measurements.

Now you're ready to get started.

  1. If the sink has standing water in it and you can't unclog it, bail out as much as you can.
  2. Place the bucket under the elbow trap to catch the water that will leak out when you start loosening nuts.
  3. Use the wrench to loosen the nuts holding the J-Bend in place. Remember: Right Tight, Left Loosen, but be careful if you have a Cast Elbow connection. The nut connecting the Cast Elbow to the J-Bend is threaded from the bottom, which will flip your perception of right and left. Remove the J-Bend.
  4. If you have a slip joint extension tube, chances are you will not have to replace it. But if you do, simply loosen the nut connecting it to the Tail Piece and remove it. Use the hacksaw to cut the new slip joint extension tube to the same length the old one was, if necessary.
  5. Throw away all the old gaskets you removed. Use your nice new ones.
  6. At this point, as long as you have your pipes removed, you may want to take the opportunity to clean out any open pipes you exposed.
  7. Finally, replace anything you removed with the new version you bought. Remember to use your gaskets and seal the threads with pipe sealing tape as described above, so you won't have any leaks. Tighten the nuts down but not too hard, you don't want to break your new pipe. If replacing the slip joint extension tube, screw it in and tighten it down before installing the new J-Bend.
  8. Wipe any water off your new pipes and then test them for leaks. Plug the drain and run the water to get a few inches in the sink, and then remove the plug. Watch the pipe, especially at the joints and at the bottom of the J-Bend, until the sink drains completely. Wipe the pipe down with a paper towel as a double-check.
  9. If any of your joints leak, remove the part completely, re-seal with new thread tape, wash off the gasket, and tighten the nut down a bit harder when you put it back. More thread tape is better, but if you use too much, the nut might not bite into the threads properly.
  10. Re-test for leaks. If you're still leaking, it might be time to call a professional.

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