When you notice water in your kitchen sink cabinet, there is a leak either in the sink drain basket or the drain pipe connection. Fixing a kitchen sink leak requires repairing either the sink drain basket or the drain line connections. Identifying the source is key to fixing the sink. Dry off the pipes and the drain basket under the sink with a towel and fill the sink with 6 inches of water. Allow the sink to drain while you inspect the pipes and drain basket for the leak. Once you identify the source, you can fix the kitchen sink and stop the leaking.
Loosen the nut connecting the sink plumbing to the sink basket with a pair of slip joint pliers. Loosen the nut between the "P" trap and the straight pipe going to the house wall drain. Disconnect the sink plumbing from the sink basket and turn the "P" trap to the side so you have clear access to the drain basket.
Turn the large nut securing the sink drain basket to the sink counterclockwise with a pipe wrench. Remove the large nut from the sink drain basket and remove the cardboard washer and rubber washer from the basket.
Tap the bottom of the basket with a rubber mallet to dislodge the plumber's putty between the sink basket flange and the sink. Go to the top of the sink and pull out the sink drain basket. Clean the area around the sink hole with a putty knife to remove the residual plumber's putty.
Inspect the drain basket flange for damage or rust. The flange is the portion of the drain basket that sits on top of the sink hole. Most often, though, drain basket leaks occur due to the plumber's putty seal cracking. If there is damage to the drain basket, replace the basket with a new one. If there is no damage to the drain basket, scrape the old plumber's putty off the bottom of the flange with a putty knife.
Place a small ball of plumber's putty in the palm of your hands and roll it into a thin rope. Place the rope of plumber's putty underneath the flange on the drain basket. If you have metal drainpipes, wrap plumber's tape around the threads of the sink drain basket. If your drainpipes are PVC, plumber's tape is not necessary.
Insert the drain basket into the sink hole with the threads pointing down. Press down to seat the drain basket in the hole. Ask a friend to hold the drain basket firmly while you go under the sink to reattach the plumbing. Slide the rubber washer and cardboard washer over the sink basket threads. If using a new sink basket, use the new washers that come with the basket.
Thread the large securing nut onto the drain basket until it is hand tight. Tighten the nut firmly to the sink with the pipe wrench. Line up the sink plumbing pipes under the sink basket. Thread the securing nut from the sink drain plumbing to the drain basket until it is hand tight. Turn the nut another three quarter turn with the slip joint pliers. Tighten the wall drain securing nut with the slip joint pliers.
Tighten the connection with a pair of slip joint pliers and run water through the pipes again. Often, especially with PVC pipe, the nut only needs tightening. If you still have a leak, loosen the connection and slide the nut away from the pipe connection.
Remove any residual plumber's tape from the pipe threads if you have metal pipes. If you have PVC pipes, loosen the opposite securing to allow pipe movement.
Wrap new plumber's tape around the pipe threads on metal pipes. Thread the securing nut back over the connection until it is hand tight. Turn the nut another three quarter turn with slip joint pliers. Tighten the opposite pipe nut with the slip joint pliers if you have PVC pipes.
Drain baskets are available at home improvement centres.