If water is leaking under the sink, the basket strainer may not be tightly sealed. To test, close the stopper, fill the sink with water, and inspect from underneath with a flashlight and a dry rag.
If the strainer leaks try tightening the locknut using groove-joint pliers or a spud wrench (below). If that doesn't solve the problem, remove the strainer, following the steps on these pages. Either clean the drain hole and reinstall the strainer or install a new strainer. A strainer made of thin metal or plastic may soon fail to seal water. A better-quality strainer costs more but will last longer. Installation is the same for all kinds of sinks: stainless steel, cast iron, or acrylic.
Time About 2 hours to remove a basket strainer and install a new one
Tools Groove-joint pliers, spud wrench, hammer, plastic putty knife, screwdriver
Skills Dismantling and reinstalling a trap
Prep Make the worksite under the sink comfortable; position a bucket to catch water
Materials New basket strainer, plumber's putty, replacement 1-1/2-inch rubber or plastic washers
Unscrew the slip nuts at the bottom and top of the tailpiece. Gently pull the tailpiece down from the strainer and remove it. Unless the washers are in very good condition, buy replacement washers. If any part of the trap is damaged, replace it as well.
Loosen the locknut with groove-joint pliers or a spud wrench (opposite). Remove the nut and pull out the strainer. Scrape the old putty away from around the sink hole and clean with a rag.
Make a rope of plumber's putty (do not use putty that has started to dry) and place it around the sink hole or under the lip of the strainer body. Press the strainer body into the hole and center it.
Have a helper hold the strainer in place while you slip on the rubber washer, the fiber washer, and the locknut. To keep the strainer from spinning while you tighten the locknut, insert the handles of a pair of pliers into the holes and brace them with a screwdriver.
Tighten the locknut as tight as it will turn. Scrape away the squeezed-out putty with a plastic putty knife to avoid scratching the sink. Reattach the tailpiece. To test for leaks close the stopper, fill the sink, and pull out the stopper.