Have a 30yr old pedestal sink that builds up black muck in the drain above the trap, and on the pop-up stopper and in overflow drain. No smell but it's insidious. Been told it may be caused by a reaction with galvanized waste line etc. We're hoping a new waste line and trap may help alleviate the problem. Also was told by plumber that they're doing away with overflow drains these days due to this problem. Just continuing to clean this out with vinegar, baking soda and then diluted bleach is not acceptable. Re-occurs every few weeks. Now we're thinking a new sink with no overflow would help. Not sure this sink is vented properly--would that enable this?