I installed two new Price Pfister 4" center faucets in our bathroom. After installing the pop-up assembly on one of them, I noticed it leaks from under the sink where the drain meets the rubber gasket. I replaced the original gasket with a larger one which would sit outside the hole instead of inside like the one which came with the faucet. It still leaks! By the way this is the only one that leaks. Why is there water there and how can I fix the leak?