This worked for me, can't say which, or a combination of the methods worked:
Pour a little ammonia down the drains every 2-3 days.
Make traps - fill custard cups with about 1/2 cup white vinegar, secure the top and sides tightly with aluminum foil, then punch holes in the top with an ice pick. I left a couple on the kitchen counter, and one in the bathroom. You'll be tempted to peek but will get discouraged. Wait 4-5 days. You'll be amazed at how many you trap. You could probably go on forever but the thought of all those little fly bodies floating on top was kind of gross, so I threw it out, and started a second application. By the second round, most were gone, and I didn't catch many after that.
I keep a spray bottle of glass cleaner, in the kitchen when they land, give them a spritz, and wipe down with a paper towel. You can catch a few that way, and your walls will be sparkling.