Installing air gap with uneven countertop bottom

[rrando]

I am installing a dishwasher air gap in a granite countertop and the undermount sink flange is very close to the hole for the air gap. So the bottom nut only contacts the sink flange on one side and does not make contact with the countertop on the opposite side. There is about a 1/8 inch difference in thickness between the sink flange and the countertop. How do the pros handle this? (Yes, I know they would have left more clearance for the air gap and faucet).

 

[Reach4]

Some would find a tube/pipe that would fit over the airgap thread, but would not fit into the hole. If necessary, the tube would be notched out on one end enough to clear the sink flange. The tube would be cut to length. Then the nut would tighten over the piece of tube.

 

[Sponsor]

 

[rrando]

Great idea. I was thinking some sort of cut-off washer, but couldn't find a really large one. As it turns out, 1.5 inch ABS pipe is exactly the OD of the nut, so I will cut off a small piece and cut a notch to fit around the flange. I may even be able to find another plastic pipe to fill the inside of the pipe. Since it is plastic, corrosion is not an issue.

 

[rrando]

Thank you Reach4. Your suggestion worked really well. I cut two 5/8 inch long rings from some left-over 1-1/2 inch ABS pipe. I removed a section about 0.9 inches from one ring so it would compress to fit inside the other. At first, I used a small hand saw to trim the ends of the split ring, but I found that a sharp knife worked better. I compressed the split ring, and inserted it just a little way into the larger ring. I used a Q-tip to apply ABS cement to both mating surfaces before pushing the split ring flush. Next I will file the assembly to fit under the countertop and over the sink flange. If I had a piece of 1-1/4 inch ABS I might have used that for the inner ring, cutting a slot if needed to fit. Here is a photo showing the ABS pipe, two assemblies - one whole ring and one split, before assembly, (I may need this for the faucet) and an assembled and glued set for the air gap with its nut, rubber washer and top. The inner diameter of the homemade ABS piece is just about a perfect fit.