Sometimes, a bad smell in the sink comes from the water and not the drain. Fill your sink with hot water only. Let it sit for a minute and then put your nose close to the water and breathe deep.
The diagnosis: If it smells bad even though the stopper is covering the drain, the culprit is probably the water heater. (You won’t smell it if you run the cold water.)
The solution: Replace the water heater’s anode rod, which corrodes over time. Sometimes called a “sacrificial anode,” the metal rod is designed to deteriorate in order to protect other exposed metals in the tank. Rods last from six months—if you over-soften your water—to six years or more.
