On Wed, 20 Mar 2019 07:58:03 -0700 (PDT),
wrote:

On Tuesday, March 19, 2019 at 12:19:24 PM UTC-6, wrote:
Septic or city sewer?

City sewer.

I suppose you could put a little insecticide in each trap to knock
them down. Once you break the cycle they will usually stay gone a
while but they are living in the sewer pipe. Be sure your traps are
staying full of water (no bad vents)