Andy, yessir.

In addition to treatments with the aforementioned drain cleaner, I also now:

-- cover all three drains in my condo , per the advice of this fellow: https://www.youtube.com/watch?v=px_f...1&feature=plcp


-- run the dishwasher once a week. The principal locale of infestation a few months ago was the 7/8" dishwasher drain hose, running from the dishwasher to the in-sink garbage disposal. I replaced the hose with a new one cut from a roll at Ace Hardware. The hose has printed on it that it is for dishwasher drains.

I now see maybe one fly every couple of days. I will cut back on all the treatments in a month or two and see what happens.