I've never had any luck with them, I always end up taking the pipes
apart and using a snake. You might also try a plunger - seal the other
side of the sink (with a wet towel held in place by someone else) and
plunge the daylights out of the other.

I called a plumber once after having dumped gobs of drano down a
bathtub drain. He came out and plunged the thing and had it fixed in a
few minutes. Showed me how to take the batchtub/shower switch thing
off and plug that hole up to improve the effectiveness of the plunging.
$50 lesson.