I've currently got a small tank set up with flourite black sand.
For maybe the first month or so, I would see areas were detritus would accumulate, but then it seemed to disappear. I've got a pretty healthy population of MTS (also ramshorns and mini ramshorns), and I suspect that once there were enough of them, their movement effectively 'churned' the top layers of the substrate, causing the detritus to get mixed in.
I currently don't see any detritus, just a handful of dead snailshells (mostly ramshorns and pond/bladder snail shells) that I haven't bothered to clean up.
My MTS don't seem to burrow deeply, they just plow through the sand a milimeter or two deep.