How to Clean the Air Gap
Many people realize the dishwasher connects to a little thing on top of the sink, some even know that it is called an air gap. However, many people wonder "what is an air gap for?" The air gap is there to prevent the water from being siphoned out of the dishwasher. When water flows through the drain hose, it creates a suction on the water still in the dishwasher. The air gap, makes a hole for air to get in. That way, the water only leaves the dishwasher when it supposed to, when it is pumped out. Another benefit of an air gap is that if the drain hose becomes clogged, the dishwasher can still pump out the water. Instead of flowing through the hose, as it should, it can flow out the air gap and into the sink. However, the reason it is in the plumbing code in some communities is that it ensures that sewage can never back up into the sink and then into the dishwasher and contaminate the water supply through the connection to the fresh water supply.
The dishwasher's drain line usually connects to an air gap mounted at the countertop level on the sink. The drain line continues from the air gap to either the garbage disposer or directly to the sink drain. If the drainage hose between the air gap and the drain is partially or completely blocked, water from the dishwasher will flow out of the air gap and into the sink.
To clear the blockage simply remove the hose and flush it out or replace it. While the hose is off, check the garbage disposer's dishwasher inlet to make sure it is clear.
If the garbage disposer was recently replaced or the dishwasher is newly installed, check the garbage disposer knock out plug. The dishwasher drain line connects to the garbage disposer and at that connection is a plug that must be removed prior to using the dishwasher. If it is left in place the water cannot drain properly and so will spill out from the air gap.
If the problem persists, it may be as a result of a slow drain. Try clearing the drain with a mechanical device. Chemicals are not very effective at clearing a slow drain because they flow through too quickly. See our plumbing section for more information.