Begin by preparing your work area to prevent water damage and ensure you have all tools at hand. Place several old towels or a shallow pan directly under the sink, positioned beneath the garbage disposal and the air gap hose connections. This will catch any residual water that drains from the hoses when you disconnect them. Gather your tools, such as pliers and a small brush, and place them within easy reach.

To access the air gap for cleaning, you must first remove its decorative cover. Most covers are either threaded or snap-on. Grasp the metal cover firmly and try to unscrew it by turning it counter-clockwise. If it doesn't turn, it is likely a snap-on cover; in this case, pull it straight up to remove it. Once the cover is off, you will see a smaller plastic cap. This cap may also twist off or simply pull up. Remove this plastic cap to expose the inside of the air gap body.

With the caps removed, inspect the inside of the air gap body for obstructions. Often, food particles and gunk accumulate here, causing the blockage. Use a small bottle brush or a pipe cleaner to scrub the inside of the air gap body. Use rolled-up paper towels to wipe out any dislodged debris. Clean the plastic cap you removed as well, ensuring any small vent holes are clear. A toothpick can be helpful for clearing these small openings.

If the top of the air gap is clean, the clog is likely in the drain hose leading from the air gap to the garbage disposal. Under the sink, locate the larger of the two hoses connected to the bottom of the air gap. Place a bucket underneath it. Loosen the hose clamp holding it to the garbage disposal inlet or sink drain tee and pull the hose off. Check the hose and the inlet port for blockages. Use a small brush or a blunt object like a screwdriver to clear any gunk. Reconnect the hose and tighten the clamp.

Once everything has been cleaned and the hose is reconnected, reassemble the air gap on top of the sink. Place the plastic cap back on, followed by the decorative cover (screw or snap it back into place). To test your work, run your dishwasher on a 'Rinse' or 'Drain' cycle. This will force water through the system. Watch the air gap closely to ensure no water leaks from the top. Also, check under the sink to make sure the hose connection you worked on is dry and not leaking.

If cleaning did not resolve the issue, or if you found the air gap body to be cracked or broken, you will need to replace it. Start by going under the sink and disconnecting both the smaller hose coming from the dishwasher and the larger hose going to the garbage disposal. Use pliers for the clamps and have your bucket ready. Next, unscrew the large plastic mounting nut that holds the air gap body to the underside of the sink. Once the nut is removed, you can pull the entire air gap assembly up and out from the top of the sink.

Take your new air gap kit. From the top of the sink, insert the threaded body of the new air gap through the hole. Ensure any gaskets included are properly seated. From under the sink, thread the new mounting nut onto the air gap body and tighten it until it is snug. Hand-tight plus a quarter-turn with pliers is usually sufficient. Now, reconnect the hoses. The smaller-diameter hose (from the dishwasher) attaches to the smaller inlet nipple on the air gap. The larger-diameter hose (to the garbage disposal) attaches to the larger outlet nipple. Secure both with their clamps.

With the new air gap fully installed, conduct a final, thorough test. Place the new decorative cover on top. Run the dishwasher on a 'Drain' or 'Rinse' cycle. While it's draining, use a flashlight to carefully inspect all connections under the sink (both hose connections at the air gap and the connection at the garbage disposal) for any signs of dripping. Also, confirm that no water is sputtering from the top of the new air gap. Wipe each connection with a dry paper towel to make even the smallest leak obvious.