How to Install a P-Trap in a Basement

P-traps are simple devices that perform an important task: They prevent sewer gas from drifting back up drainpipes and getting into your home. A P-trap consists of a curved piece of pipe shaped like a "U" and a section of pipe called a trap arm. You can either install a P-trap on a sink or an appliance in your basement, or you can install it as part of the installation of a shower.

Sinks or Appliances

Step 1

Locate the drain body under the sink you need to hook up to the main bathroom drainpipe.  The P-trap connects to the drain body, and the trap arm connects the P-trap to the drainpipe.

Step 2

Place the washer against the mouth of the drain body on the underside of the sink.  Slide a coupling nut over it, and attach the P-trap to the drain body using the nut.

Attach the trap arm to the P-trap using the same washer and coupling nut combination, and repeat the process to attach the trap arm to the drainpipe stub out at the wall. 

Step 3

Follow the same steps for installing a P-trap on a clothes washer.  The only difference will be in the size of the P-trap.

It needs to match the size of the drainpipe in the wall. 

Shower Drains

Step 1

Install the P-trap before installing the drain assembly or laying the floor for your basement shower. 

Step 2

Use a trowel to dig around the drainpipe servicing the shower to free it of soil or gravel.  Expose the end of the pipe beneath the shower stall, and wipe its mouth clear of dust or debris with the damp cloth.

Step 3

Connect the P-trap to the trap arm using the washer and coupling nut.  Attach the trap arm to the drainpipe.

Step 4

Install the shower drain assembly, connecting the drain body to the P-trap whenever you are ready to put in the shower. 

Things You Will Need

  • P-trap
  • Nylon compression washers
  • Coupling nuts
  • Trowel
  • Damp cloth


  • If the P-trap will be exposed to view instead of being hidden in a cabinet, use a chrome or copper trap assembly. If it is hidden, PVC assemblies are strong enough to service your home.