How to change an Elbow Drain Pipe under a Sink

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The reason the elbow drain pipe is there is to prevent sewer gases from wafting into the kitchen.
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The kitchen sink P-trap, which is the under-sink elbow pipe connected to the drain, is filled with water. The reason it's there is to prevent sewer gases from wafting into the kitchen. The P-trap is a nifty little invention that has made hygienic plumbing possible, but it does tend to collect debris. Because of this, it needs cleaning and may have to be replaced every so often.

Nowadays, most P-traps are made of PVC plastic, but older ones were chrome-plated steel, cast iron or brass. If you have a chrome P-trap in the kitchen, now is a good time to replace it even if it isn't corroded. If you wait, you could end up dealing with a leak at an inconvenient moment, such as in the middle of a party.

P-Trap Connections Should Never Be Glued

When you examine your under-sink elbow, you see that it's joined to the tailpiece, which is the vertical pipe coming from the sink or garbage disposal, and to the horizontal waste arm by large connecting nuts. You're supposed to be able to loosen these nuts by hand, but you seldom can. You usually need to use slip-lock pliers or a wrench.

The nuts may be difficult to turn, especially if the P-trap is metal and the metal has corroded. They should never be glued, though, so have confidence that you'll be able to loosen them if you use enough force. If someone made a mistake and glued the connections, or the corrosion has made turning the nuts beyond your powers, get out your hacksaw because the only way to remove a P-trap glued together or stuck with corrosion is to cut it out.

Removing the Kitchen Sink Trap

You don't have to turn off the water before removing a kitchen sink trap, but you may want to close the drain just in case someone inadvertently turns on the faucet. With the cabinet cleared out and your headlamp in position and turned on, you're ready to go:

  1. Loosen the compression nut holding the trap to the tailpiece. Try to do it by hand, and then use a wrench or locking pliers if needed. Unscrew the nut all the way and disengage it from the mouth of the trap. While you're at it, make the assembly easier to remove by loosening the nut in the middle of the trap just above the elbow so the trap can swivel.
  2. Unscrew the nut on the horizontal arm of the trap on the opposite side of the elbow. The trap is now free, and you should be able to remove it by pulling the mouth away from the tailpiece and the entire assembly away from the wall. Be careful because water will spill out.
  3. Hold the trap upright while you remove it from the cabinet. Take it outside and turn it over to empty it. Yes, it will be gross; that's par for the course.

Installing a Brand-New Under-Sink Elbow

To install a new P-trap, you'll just reverse the procedure for removing it, but there are a few pointers to keep in mind:

  • Most P-trap assemblies are 1 1/2 inches in diameter, but your sink tailpiece may only be 1 1/4 inches. To make the connection, use the extra-thick flange that comes in the P-trap kit.
  • Hand-tighten all connections and then test the trap by running water through the sink. Use pliers to tighten the nuts only if the trap leaks. If the trap doesn't leak, congratulations, you don't need to do anything else.
  • About an inch of the tailpiece should fit into the trap opening. If the tailpiece is too long, cut it shorter. If it's too short, purchase and install a tailpiece extension.
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Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in 2010. He worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at Hunker.com.

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