Fill clogged basin with enough water to cover head of plunger. Coat lip of plunger with petroleum jelly (this helps create better seal). Slide plunger's cup over drain opening, then rapidly pump plunger up and down. You should feel water move in and out of drain. It is this back-and-forth water pressure that can eventually build up enough force to dislodge whatever is blocking drain. After about a dozen firm strikes, jerk plunger up quickly. Water should rush out. If it doesn't, try same procedure two or three more times before attempting another method.