We received new brass assemblies for our bathroom sinks. They seal real well at the sink(with thread dope under the rubber seal), the stopper ball seals well, and the big rubber washer/nut seals good under the sink. However, the tubing that threads into the body above the p-trap won't seal; even with thread dope on it. I've got three more to use eventually. Any help? Solder it together? Probly the best idea I'm thinking. Thanks for the help!