P-Trap Anatomy

• The P-trap on most sink drains consists of a vertical connection, a horizontal one and a pipe with an inverted "P" shape between them. The vertical end connects to the drain tailpiece, which is the extension of the drain just below the sink, while the horizontal end leads to the waste line. The assembly includes a swivel connection so the trap can be oriented with the existing pipes. Compression fittings that consist of a nut and a tapered washer hold the ends of the assembly to the tailpiece and waste line. The washers are usually plastic and must fit tightly to be effective.
  
  

Leaking Connections

• If water is leaking from your P-trap, the chances are that it is coming from the compression fittings on either end, and the cause is usually a blocked trap, a loose connection or both. If the trap is partially blocked, water backs up as the sink is draining and, if the connections aren't watertight, it will seep through and drip onto the floor. If the connections are loose enough, water will seep from them even in the absence of a blockage in the trap. The solution is to tighten them or replace the washers.
  
  

Tips for Tightening Trap Connections

• The compression nuts on either end of the trap, as well as the swivel nut, are designed to be hand tightened, but if you need more force to stop a drip, a pair of slip-lock pliers usually helps. It's important not to over-tighten the nuts, however, because you may strip the threads and, if you do, you'll need replacement parts. If a leak won't stop, disassemble the trap and clean it. An inspection of the washers may reveal enough wear on one or both of them to warrant a replacement. Once the trap is clear and the washers secure, the compression fittings should work.
  
  

Troubleshooting

• A secondary purpose of P-traps is to catch small items that may unintentionally fall into the drain, but other debris can also collect there, eventually creating a clog. Remove your traps periodically and clean them to prevent these clogs from causing leaks. Leaks can also result from pipes that fit together at a slight angle, which can happen when the tailpiece and waste line are offset with respect to each other. If no adjustment is possible that will straighten the pipes, it may be possible to insert an angle fitting or flexible pipe between the end of the trap and the waste line.