We are trying to install a new Staron double bowl lavatory vanity top. We have put in a Moen Asceri faucet with pop up drain. They have included a plastic adaptor for the drain to hook the overflow tube from the sink, and you put it between the sink underside and the tailpiece. It is white plastic and has rubber gaskets that the overflow tube screws into, but no matter how we install it, it leaks. There were no instructions, and we have a flat rubber washer, and a more rounded smaller rubber washer. This piece is round but does have one flat part that does not fit the seal. Does anyone have any suggestions. Or where we could get parts that would work.