You can go onto thurston counties website and pull up all recorded information of a septic system with a parcel number for said property or you can go to Planning and develpment at the Thurston county courthouse from 8am-12pm monday through friday and they will pull up information and print it out for you.
The County typically has the current test, pumpers reports and septic as builts along with the water samples from your local water company.
Not sure exactly about the rules in your state (Washington) as I am in California. You can always put the property back on your local MLS "pending cancellation of existing transaction" and then give the buyers a deadline to perform. If they do not meet the deadline, than you will have not lost any time seeking out new offers. Loans do take awhile these days, BUT 60 days should have been more than enough time for a qualified buyer with a top notch lender.... more