I have a 1964 duplex. For the last few weeks water wouldn't go down in the bathroom sink, then it got worse, gunk started filling up the sink when I wasn't even home. The bathroom in both units are back to back and obviously share some plumbing since their water won't go down the BR sink either. I tried the salt, baking soda and vinager flush 3 times. It didn't help at all. I had a plumber out finally, and he said there was no visible way to remove the debris, and that a snake would just push up into the other unit sink, not down the pipe and in summary my Home Insurance Policy won't touch the problem. He said I might have to go through the roof to fix this. Help!