If you have a double unit and find your kitchen sink clogged on both sides, it usually means the blockage is in the drainpipe below the point where the pipes for the two sinks join. This makes it much easier to understand what you need to do to clear the actual clog. There are a number of actions you can take but they all equate to a fairly simple job.
Step 1 - Plunger
Start by using a sink plunger if your kitchen sink is clogged. With a double sink unit, one of your sinks will house a garbage disposal. Fill that sink about a quarter full and plug it; you shouldn’t use a plunger on that side of the double sink. Now fill the other sink about a quarter full of water as well. Start using the plunger by pushing down hard to form a good seal over the drain before continuing. Check the other sink to make sure the plug is still in place as is this forms a seal to help the vacuum.
After you’ve plunged about five times, stop and see if the water drains. If it does, remove the plug from the other side to check that both sinks drain. Run hot water down the sinks for five minutes to ensure the lines are completely unclogged. If the plunger doesn’t work and the kitchen sinks are still clogged, repeat the process several times to see if further plunging helps.
Step 2 - Removing the Trap
The most likely place for the kitchen sink to be clogged is in the trap, which is the bend under the sink that’s shaped like a “U.” Clear out the cabinet under the kitchen sink and place a bucket under the pipe. Use a wrench to loosen the pipe before easing it off. At least a small amount of water will drain into the bucket.
Inspect the pipe you’ve removed and use a wire coat hanger to push any debris out. If the pipe is clogged, this will usually be in a thick mass. Take the pipe to a different sink or an outside hose and wash it clean after clearing it. Replace it and run water through the sinks to ensure that this was the only clog. If the water still drains freely after five minutes, your job is finished.
Step 3 - Snake
If these steps don’t work, you’ll probably need to use a sink snake. You can buy a snake for home use or you can rent a more expensive, professional model from a store called a plumber's snake. Whichever you use, wear gloves during operation as this will save the skin on your hands from becoming damaged. Feed the cable slowly down the kitchen sink and the pipe, continuing as far as you can before bringing it back again. Repeat this process several times, feeding in the snake and pulling it back out very slowly. This should penetrate and remove the clog.
Check your work by running water in both sinks for several minutes. If the water drains cleanly and freely, the kitchen sink clog has cleared. Don’t use chemicals in your sink to clear the clog as these can end up contaminating the groundwater.