Don't know if you've watched the British series "Doc Martin" on PBS, but there was an episode with just that same scenario causing several people to come down with cholera like symptoms.Suddenly I'm worried about back flow.???
Should the dishwater be that brown?!!
Doc Martin is my all time favourite British (very dark) comedy.
I tried to find a clip of that particular episode, but unfortunately it isn't available for viewing outside of the UK.