I used ammonia to clean out and kill off any gnats in the drains. In the process, I discovered the shower drain needed a good scrubbing anyway. (I hadn't removed the drain cover in awhile.)
The kitchen was clear of flying insects first thing this morning. but I saw gnats a little later. Then I went into the small bathroom with the newly scrubbed shower drain and saw gnats flying near the ceiling.
A friend suggested Raid---said it cleared them out for her. (Gnats seem to be the curse in this area this year.) It worked, but I'm glad I got my shower drain scrubbed! Just in case the few flying around feel like multiplying, I have a spare can in my laundry closet. I hate using it in my house and then having to scrub everything again, but I hate having bugs in my house more.