First of all, Hello, my name is Simon. (You're gonna have to try pretty hard to come up with a joke that hasn't been thrown at me yet)
I have a subfloor replacement that has turned into something more interesting. The replacement is due to septic pump failure and grey water backup into the basement(concrete slab).
So far I have taken about two 5gal pails of dirt from under the wood subfloor and havent found an obvious spot where the dirt is coming from. I still need to take the shower out so I can see and clean the full area today.
Very sandy soil, no sewer smell but was used daily up til a couple weeks ago. Laundry, shower, toilet and vanity.
Just looking for some guesses right now, I report back later with more info but I'm thinking broken drain line. Also, this is not in the area of the original backup issue.
So much for a short first post and now I going to try and attach pictures too, or just check the album...
What is happening is there is a break in the sewer main and dirt is getting into the pipe. The dirt is either causing a blockage (or something else is) and it's causing your sewer main to back up. The backing up water carries the dirt along with it.
I've seen this a few times out in the field.
You need to get someone out there with an inspection camera and locate the break. It'll have to be dug up and fixed! Just pray it's in a good spot!!!