A plunger is the first tool to reach for when a sink gets clogged up. But to get the most out of your efforts, try these tricks of the plumbing trade: First, stuff a wet rag into the sink overflow hole so that all of the plunger power goes directly to the clog. Also, remove the pop-up drain plug and, if possible, fill the basin about halfway with water. Then coat the lip of the plunger with petroleum jelly to form an airtight seal against the bottom of the sink. Pump the plunger up and down several times, making sure you don't break the seal with the sink. Then quickly yank the plunger off. Repeat this four or five times, or until the clog is cleared. If the obstruction remains, remove the trap below the sink and snake out the drain line with a cable auger.