This is technically an inside the home issue but not sure where to turn. This house is new to us almost 3yrs old.

The prior owners we knew had the bathroom sewer line replaced and rerouted around the outside of the house. They failed to tie in the upstairs bathroom to the old SHARED sewer line. After buying the house and within a few months a mound in the floor was clearly felt in our master bedroom/bathroom. Drove me nuts but we finally discovered the issue as we were having the old pool removed. SO we know all the upstairs bathroom waste water was filling up the dead line that ran under our bedroom.

This year we started seeing multiple soldier flies in our bathroom only. I observed them outside in the backyard going into a hole in the soil near the old drain line. All made sense, lots of material for them to feast on there and the gaps under the walls in the bathroom where the floor rose and fell allowed them to sneak in. And I finally observed one crawling from under there. Sealed all the floor boards and no more soldier flies in the bathroom - YAY.

NOW they are all in the kitchen on the opposite side of the house and upstairs. I know there are gaps in this old house. But this part of the house is all remodeled and I made sure to seal all the walls around the floors so who know where they might come in from. They could be traveling up the wall by the bathroom line across the house and coming in absolutely anywhere and just travel to the 2 large windows and brightest areas.

So i need to address the source which is the poop filled soil under my house :(

Is there any chemical that can be sprayed around the house that kills soldier flies? Anyone ever hear of injecting anything into the soil? It's driving us crazy.