Step #5: Attach Locknut to Strainer
Remove any excess putty from the bottom of the sink opening and strainer, then slide the rubber washer onto the strainer from underneath the sink, followed by the friction washer.
Thread the locknut onto the strainer (turn clockwise), being careful not to cross the threads, and hand tighten the nut as much as possible against the friction washer and gasket.
Insert either a special basket strainer wrench or needle nose pliers into the bottom of the strainer opening to keep the strainer from turning, and use a locknut wrench or large pipe wrench to tighten the locknut up against the sink.
Snug the locknut up tight but don’t over tighten, which could break the locknut or strip the strainer threads.