My neighbor curses at her 12-year old child for various infractions and occasionally leaves her alone in the house into the wee hours of the night, so I felt a note about her drain would be less confrontational than a "face to face" discussion.

After reading my note, my neighbor procured a maintenance man the very next morning. He poured dirt into the water (and managed to track some of the mud onto my property). It took a few days for the smell and water to disappear. She still hasn't fixed her drain. I did contact L&I as a follow-up; I'm not sure if the inspector came out while I was at work.