P-traps are U-shaped and are found under sinks, showers, bathtubs and in washing machine sewer lines. Their job is to collect and sustain water in the bend to stop sewer gases from traveling up the pipe and into the room. P-traps come in various diameters to fit different water fixtures, and although sink P-traps are generally screwed into place, traps for the other fixtures can be cemented. Replacing this type of trap requires that you cut out the trap before cementing a new one into position.
Things You'll Need
2 straight PVC couplings
Mark the PVC pipes attached to each side of the P-trap three inches away from where they join to the trap. Make a straight perpendicular cut through the sewer pipes at both marks, using a hacksaw. Remove the trap. Scrape off all plastic burrs from the cut pipe ends with a utility knife.
Cut two sections of PVC pipe (5 inches or longer) that are the same diameter as the existing pipe. Remove burrs. Apply PVC primer to one outside end of both pipes and the inside ends of a new P-trap. Apply PVC cement to all primed areas and push the cemented pipe ends into the ends of the P-trap. Hold in place for five seconds while the cement dries.
Hold the new trap with pipes in position against the existing cut pipes. Mark both pipes attached to the trap where they will connect to the existing pipes. Cut through the pipes at both marks. Remove the burrs.
Apply PVC primer to the ends of the existing cut pipes, as well as the ends of the pipes attached to the trap. Also prime the insides of two straight PVC couplings. Apply PVC cement to all primed areas. Push the couplings onto the ends of the existing pipes, then push the pipes connected to the trap into the other ends of the couplings. Hold in place for five seconds.
If installing an ABS P-trap, use only ABS cement. No primer is necessary. If there is room, cut the sewer pipes with a handsaw, as it is easier to make a straight cut.