Let me save you the $165 I just paid the plumber for this advice: no Draino, especially if you live in an old house with old pipes. Unless the directions are followed perfectly--and sometimes, not even then--it won't work and actually makes the problem worse because Draino (or other products like it) clump up and cake on pipes. The plumber's exact words were, "We (plumbers) love that stuff!" Of course they do--it keeps them in business!
Instead, pour two cups of straight bleach down your drain. Wait 30 minutes and flush thoroughly with hot water. I haven't tried this method yet, but the plumber swears by it.
Do you have a tried-and-true method for unclogging sink drains? Does the bleach method actually work?