If your sink backs up, follow a few basic steps to try and unclog it without resorting to chemicals or a plumber.
Many people buy an assortment of liquid or chemical drain cleaners, but a plumber will tell you that some of them can eat through your pipes. The best way to get your sink working again is to use a plunger. First check and make sure you don't have an overflow. Often a bathroom sink will end up this way, but kitchen sinks usually don't.
Next, stuff some rags in the drain opening. Now see if you have a stopper in the sink; if so, remove it. But if you have a lever, make sure it is in the open position. Check and see how much water is in the sink after you place the plunger directly over the drain hole. Make sure you have enough water to cover the cup of the plunger. Now pump the plunger ten times rapidly. Pause to see if the water is draining. You may have to do this three or four times to get results.
Now remove the rags and replace the stopper. If this does not work, you will have to remove the trap under the sink. Make sure the drain stopper is in. Then place a bucket under the trap. Put a pair of slip joint pliers around the slip nut and turn counter clockwise until it is loose. Do the same on the second nut. If it is copper piping then slide the slip nut down and remove washer. For PVC piping, remove the slip nuts and washers. Then remove the trap and clean it with a small bush or try to run a rag through it.
Next, remove your stopper and let the sink drain. If the washer or trap is in bad shape, take to the hardware store to get matching replacements. Now attach a new trap; first slide the slip nut and then the washer with the tailpiece. Connect the straight end of the trap with the tailpiece. Slip a washer over the joint and the slip nut on top pf the washer. Tighten by hand. Put a slip nut and washer onto the trap's arm. Connect the bend of the trap with the arm. Slip the washer and then the nut over the joint and tighten. Now take pliers and tighten both nuts. Check for leaks after you turn on the water.
Whether your sink has a simple clog or a major logjam, tackle it one step at a time until you find out what's causing the problem. Consider using a wire net to catch debris in all household sinks and avoid further problems.
