Bad news.......waste tanks do NOT have overflows
So either:
1) You have a crack in tank
2) Toilet drain line to tank is not sealed where it connects to tank...some are glued/some use a grommet/gasket
3) Vent line is not sealed where it connects to tank....some are glued/some use a grommet/gasket
4) Toilet drain line to tank is cracked and overfilled tank leaked out of this line into compartment. OR vent line-----if it runs thru compartment.
Personally I would suspect item 4.......if any of others nasty water should have run down around tank, leaked out onto ground (or at least cause underbelly to sag). Don't see how it would have gotten basement compartment carpet/floor wet.
Really do need to open underbelly........for this I would remove one section under waste tank area (vs cutting a window)
NEED to ID source of leak. And remove/replace any wet/stinky insulation.
Clean up........
I would remove the carpet
Bleach floor/wood and air dry.
Then some indoor/outdoor carpet from big box hardware
