I have a Bathroom sink overflow that has been clogged for over 20 years! I realized I need it to have it working properly so I have been trying to "Open It up" I have tried using CLR and the sharp end of a coat hanger wire but no go. Is there a small snake or tool that can be attached to a drill to bore out the clog? I don't know what other chemicals I could use. Thanks
If you can get a plunger to seal over the overflow hole, you might be able to force some air in there, or vacuum some air out, and dislodge the clog.
These things are very inexpensive and might work where the wire hanger did not. Some are more flexible, some are pretty stiff. You might also try a flat steel drain snake, just be careful and don't apply too much force.
I have not had much luck cleaning bathroom sinks from the top, I have found it ends up being much easier to pull the drain and work from the bottom where the overflow enters. All the gunk is usually packed at the bottom and in 1 case the solid section of the drain was partially blocking the overflow, I would not have found that if I did not pull the drain. Depending on how the drain is sealed you may need some fresh plumbers putty to seal it back up but if an o ring they can usually be cleaned and reused if in good shape.