Need input on weird plumbing problem

[97RangerXLT]

get some dirt and pack the dirt under the concrete before replacing the concrete that was crumbled out. if you need to go back in there and tear it out again, it will be easier to do than if you have a 10 inch thick concrete boulder...

the spray foam idea is pretty good too.

AJ

 

[Jim Oaks]

So it turns out that there is a pipe inside that pipe. Not sure why there's a lip like the pipe ends, but if you reach further, you can feel a pipe inside that one. I'm going back to my original idea that it's the drain from the upstairs bathroom.