 I think that probably the first thing I would do is have a septic inspection done with an examination of the field to check the percolation of it. Because if it's not percolating, if it's not draining properly, you could be spilling a lot of effluent into the ground unknowingly without it having a chance to really soak properly back into the soil. I think what we're hearing here is a potential failure of your septic field more than a problem with a sinkhole.