There are two washers common to PVC plumbing. A flanged washer often sits where the PVC pipe connects to the sink drain basin of a kitchen sink and the tapered slip washer that seals the connections between the down tube coming from the sink and the connections of the P-trap. The tapered washer is the more common of the two as it is used on all sinks using a removable P-trap. If you install the slip washer improperly, the joint will not seal allowing water to leak from the connections.
Things You'll Need
Drain assembly kit
Wipe the PVC pipe with a clean rag to remove light dirt from the pipe's surface.
Place the flanged washer onto the top of the flanged down tube, with the down turned edge resting inside of the PVC pipe.
Secure the down tube to the base of the sink per the drain kit installation instructions.
Slide the slip nut onto the down tube, with the threaded inner section of the nut facing the bottom of the sink cabinet.
Hold the slip washer in your hand, with the tapered side of the slip washer facing down.
Place the slip washer at the base of the down tube, ensuring that the thicker end of the slip washer facing toward the pipe.
Push the slip washer onto the PVC pipe and slide it one-inch up from the pipe's bottom edge.
Repeat the procedure to install the slip washers at each PVC connection.
Connect the PVC pipe as described in the assembly instructions.
Turn on the water and check each slip connection for signs of water leaks. If you find a leak, undo the connection that leaks and ensure that the slip washer is installed properly, with the taper of the washer facing toward the connection.