We are installing new countertops, faucet and sink. The current dishwasher has the top-of-sink vent. Do we have to install the air vent on top? If not, how do we put in another vent? I will need to check with the city of New Berlin. I'm assuming we need a vent because it's been there since we built 26 years ago. Please advise.

as restrictive as massachusetts plumbing codes are, we are not required to use an air gap for a dishwasher. as far as i know, no one has died from the bubonic plague because of this..

But you should follow the dishwasher installation instructions and install a drain 'high loop' under the countertop.

Many, many homes with dishwashers do not have an air-gap device on the dishwasher discharge line. And those that do have one sometimes have problems with it getting blocked by the food particle gunk that your dishwasher puts out after washing the dishes. I wouldn't install one, especially if it isn't required in your area. I would only install one if it is required and you will be selling the home. If you decide to sell the house later you can always add it then, they make them that mount under the countertop out of sight, it is easy to add.

As mentioned earlier, run the DW discharge line up high in the cabinet under the kitchen sink, then it drops down to make connection to the drain.

Here's a couple of drawings showing dishwasher installation without and with an air-gap device. Notice on the closeup of how the air-gap is built, you can see how food particles over time will build up at the gap, depending on how well you scrape the plates, pots and pans before putting them into the dishwasher. The bottom of the dishwasher in the pump area has a small food chopper that partly mashes the food into smaller particles so they will go out the drain hose.


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Edited 2 times.

The air gap should be above the overflow level of the sink so the bottom graphic is correct technically.