A clogged sink with a disposer presents a couple of problems. To use a plunger you must compress a large volume -- the amount in the disposer -- and you have to keep the pressure from simply escaping out the dishwasher drain hose. The method shown here will take care of the second problem. You can't remedy the first one.
Clamping the dishwasher hose creates an imperfect seal and can crack the hose. Then you're left with a plugged drain plus the need to replace the hose.
The easiest and least time-consuming method is to remove the P-trap, the probable location of the clog. But removing the trap is a little messy, and the other methods may forestall this necessity. If you don't want to go to the trouble of plugging the dishwasher nipple, go straight to the section about removing the trap.
Fill each side of a double sink with about 4 inches of water, leaving the drain on the disposal side open and plugging the other drain with the rubber sink stopper. Have a helper hold the rubber stopper firmly in place. Set the plunger on the drain opening at an angle and put pressure on the plunger to expel the air from under it. Keep the plunger flange firmly seated on the drain opening and work the plunger vigorously up and down, pulling the plunger up sharply after several strokes. Repeat until the clog is free or try another method.
A clogged disposer can be made worse by something jammed in the blades. If the disposer hums but won't run, it's jammed. Turn off the power to the unit, insert an impeller wrench into the square hole at the bottom, and work the wrench back and forth to try to dislodge the jammed article.
Turn the power on and reset the machine (see Step 3). If the motor still hums, shut the power off and push a piece of old broomstick (about 2 feet long) into the drain until it contacts the bottom of the disposer. Holding the stick against the side of the drain, push it in a circle to turn the impeller.
If the broomstick spins the impeller, remove the object with tongs, a magnetic wand, or a piece of duct tape stuck in reverse on the end of the stick. Don't try to get the object with your hands. Reset the disposer. If this method doesn't unjam the unit, it's time to call a pro.
If none of your attempts to unclog the drain is successful, set a bucket under the P-trap and remove the trap. Remove the waste clogging the trap and reassemble the trap. If the unit still does not drain freely, remove the trap and extension pipe and try working a hand auger into the clogged area within the pipe in the wall space.