Air Gap / Overflow

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    • #273147

      Does an air gap / overflow keep a back flow of waste water, should the disposal drain clog up , from entering the dishwasher? If so how do you install one if you have a drinking water system that uses the fourth hole (in a sink made for a three hole faucet). In other words, once the drinking water system is installed there is no no longer a hole for the air gap?

    • #286984

      You have to carefully drill another hole or get a single hole faucet so you can use one of the other three holes. If your drinking water faucet has the small shank, it may be easier to drill a hole for it and use the original larger hole for the air gap.

    • #286985

      HJ is right if you want to drill another hole in your sink you must first determine what kind of sink you have. I have drilled through thousands of sinks. Cast iron sinks are thick and will be covered porcelain you can tell very easely if you sink is cast iron. Look at the underside of the sink and take your hand and knock on it. If it’s like knocking on a cinder block wall its cast iron. For porcelain clad steel sink doing the same will reveal the sound of knocking on a steel door. Stainless steel is pretty self-explanatory.

      What to use to drill through?

      Cast Iron: Use carbide tipped masonry bit. Drill it in stages I will first use a ¼” drill to make a pilot hole then graduate to a ½” bit. I always use strips of electrician’s tape over the drill area to keep flaking on the porcelain to a minimum. Do not push the drill through to fast let the drill do the cutting. Place a wet napkin under the drill area inside the cabinet to catch the black dust from drilling this will make cleaning it up much faster. Buy a good drill bit not a $3.00 one buy the $8.00 masonry bit.

      Porcelain clad steel: The hardest sink to drill by far. This takes a little more precaution use lot of tape over the drill area. Only use high-speed drill bits on this type of sink. Again let the drill do the work. If you are making a hole larger than ½” use a relton drill take your time this sink is unforgiving.

      Stainless steel: Easy to do use high-speed steel start with a ¼” bit and next use a ½”. If you were cutting a 11/4” hole for an air gap faucet or dishwasher air gap assembly I would recommend using a knock out punch. This is the same type of punch an electrician would use to make a hole in an electrical box.

      I would recommend, if you are drilling a hole larger than ½” using a Relton bit. This drill has three different drills, first you make a ¼” pilot hole don’t forget the tape first, then using the larger diameter drill that has springs to aid in the cutting of the porcelain so you don’t push too hard. The second drill makes the hole in the porcelain only. The last drill is slightly smaller than the second and it will drill all the way through the cast iron. You can purchase this drill on my website at

      Good luck

      David Walling

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