Originally Posted by steamyb
The OP wrote about a 'urine smell'. Unless you pee in the sink, I don't think any solution to the OPs problem has been offered. I'm not a plumber and, yes, I have peed in some sinks on occasion. But I do remove the dishes first!
Actually yes, the OP's problem was addressed very early on.
Problem: urine odor emanating from under the sink.
Solution: Replace black tank vent located under the sink.
The thread does get confusing because it was hijacked along the way.