If your kitchen sink strainer assembly is worn or leaking, you should be able to install a new one without too much difficulty.
Step 1: Place a bucket or towel beneath the sink drain line and use a pipe wrench to loosen the drain line coupling nut from the underside of the existing strainer basket assembly. Remove the tail piece and trap from the strainer assembly.
Step 2: Loosen the locknut which holds the assembly in place by tapping its notches with a flathead screw driver and a hammer, turning it counterclockwise. If the basket assembly spins freely as you try to loosen the locknut, have someone hold the basket in place from the topside of the sink.
Step 3: Remove the fiber washer and rubber washer from the underside of the old strainer assembly. Use a flat head screw driver to carefully pry the assembly up and out of the sink.
Step 4: Clean the sink opening thoroughly. Use a plastic putty knife to scrape away any remaining putty.
Step 5: Remove the lock nut and washer from the new strainer assembly. Roll a handful of plumber’s putty into a quarter-inch thick rope. Wrap the putty around the underside of the strainer assembly. If the sink is marble, granite or another porous material, use a 100 percent silicone caulk in place of the plumber’s putty.
Step 6: Place the strainer assembly into the sink opening and press it into place.
Step 7: From the underside of the sink, coat the strainer threads with pipe dope to facilitate the future removal of the lock nut. Slip the rubber gasket up over the threads, followed by the fiber washer.
Step 8: Hand-tighten the lock nut onto the strainer assembly. Use a flat head screwdriver and a hammer or a strainer basket wrench to tighten the lock nut.
Step 9: Once the lock nut is completely tightened, wipe away the excess plumber’s putty that has seeped out around the strainer assembly edges.
Step 10: Reattach the tailpiece and trap.
Step 11: Run some water to test for leaks. If a leak appears reposition the strainer basket assembly and apply additional plumber’s putty to ensure a good seal.