REPLACING THE DRAIN IN A VANITY SINK

I've been replacing all bronze parts with plastic to prevent the corrosion and rotting due to dissimilar metals.  Place a basin below the pipes in your bathroom vanity.  Loosen the nut that holds the drain in place with a wrench.  Loosen the nut that holds the trap to the drain.  This can be done by hand.  Use gloves to disassemble because it could get messy.
Now  you can remove the drain.  Clean the hole of any remaining putty or sealant that may be clinging to it.  The replacement kit (Lowes offers a kit with a softer gasket and better fitting parts) is called Pop-up Assembly with Lift Rod Plunger and Linkage.  Also purchase a tube of the GE Silicone II clear kitchen and bath sealant.  It's handy to have for other chores.
The parts are shown at the right.  In order, sealant, linkage, handle and drain tube.  The ball rod is shown in the picture on the right.
Unscrew the ring from the top of the drain tube.  The large hole in the drain tube allows the overflow from the sink to drain out.  Don't remove the blue plastic film yet.  It will protect the chrome plating until you are done.  Apply the sealant liberally around the ring as shown.
Place the ring at the bottom of your sink and screw the drain tube back into it.  Compare the ball rod (the part with the ball) to your original part and cut off the excess rod from each end of the rod with a hacksaw so that it fits.  Drop the plunger into the drain at the bottom of the sink, align it and insert the short end of the ball rod so that it activates the plunger.  Place the tapered washer against the ball and tighten the nut by hand.
Fasten the linkage to the handle by tightening the nut with your ratchet socket wrench.  Insert the ball rod through one of the holes in the linkage using the clip to retain it in position.
Reattach the trap and tighten with a wrench.  Keep the wrench and basin handy for a while until you are sure that the nuts are tight enough to prevent leakage.  Wipe away the excess sealant.
Peel away the blue plastic film from the ring and the plunger.  Your job is done.  Aren't you pleased with yourself?
If in doubt about any step in the process, please refer to the clear description of this assemble at hammerzone.  It is the section called Bath Vanity and Lavatory: Part 2 - Connecting The Plumbing