Where did you get the white connector????
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It's a piece of PVC that was heated and pressed into an oval so it would fit into the back of the foot. The inside lip was gound or tapered some to make flow a bit better and the gap around the outside was filled with expanding foam and trimmed off.
Whatever size that the SB supplied dust hose fit around. I think it was 3.5" od. No Idea what schedule it was, just standard off the shelf PVC pipe. As long as it fit, it didn't matter.