How to Replace the Drain Trap on a Sink

A drain trap is the looping section of pipe in a sink drain assembly, located just below the sink. It is required by plumbing code and is often part of installing a new sink since an old trap assembly doesn't always fit the new sink configuration. When parts of a trap corrode or the joints begin to leak and can't be fixed by tightening the connecting nuts, it's time to replace the entire trap assembly. The techniques for replacement are easier to understand if you know how a drain trap operates.

How a P-Trap Works

A drain trap is often known as a P-trap. The name is derived from its shape—a looping configuration that looks like a sideways "P." The bend in the trap holds a small amount of standing water that's left behind in the drain each time the sink is used. The water seals the drain opening and prevents gases from rising up from the sewer system into your house. The drain trap also provides a convenient recovery point if a ring or other small valuable goes down the drain. Such objects often remain in the trap rather than getting washed into the main drain. As an added bonus, the drain trap provides a place to clear clogs—either from the trap bend itself or in the branch drain leading into the wall.

A new drain trap assembly, often sold as a kit, usually includes two or three major components: the trap bend (by itself, it's shaped like a "J") and the trap arm, which has one curved end that fits into the trap bend and a straight end that connects to the branch drain opening in the wall. Some kits include a tailpiece extension that extends straight down from the tailpiece that's connected to the bottom of the sink.

Kits may come with additional adapters and parts that you may not need. The various drain trap parts can also be purchased individually.

The trap bend and trap arm are secured with short, large-diameter nuts called slip nuts. Inside each joint, a vinyl slip washer seals against the pipe. You can loosen the nuts by hand or with tongue-and-groove pliers. If you don't have pliers, you can use a pipe wrench, but be careful not to damage the parts; pipe wrenches can exert a lot of force.

Drain Trap Materials

Sink drain traps are commonly made of white PVC, black ABS plastic, or chromed metal (brass or copper). When replacing a trap, you can use the same material as the old trap or choose something different. Replacement drain traps are sold as kits at home improvement centers, hardware stores, and online retailers. Several sizes (pipe diameters) are available, including 1 1/4-inch, 1 1/2-inch, and 2-inch. Bathroom sinks usually use 1 1/2"-inch traps, while kitchen sinks usually use 2"-inch traps. Washers are provided that allow you to connect to the 1 1/4" tailpiece from a sink. 2-inch traps are commonly used on shower and tub drains. Check your drain fitting and branch drain opening to determine what size of drain trap you will need.

Some sink drain assemblies are made with rigid PVC or ABS pipes and fittings that are permanently solvent-glued at the joints. To replace this type of assembly, you have to cut off the old pipes and use adapters to connect to a new assembly with slip fittings.

Before You Begin

Set a small bucket under the trap, and have a few rags or towels ready for containing spills. The space under a sink cabinet can be dark and cramped; a small work light or flashlight can be helpful.