The more I deal with septic systems the more I know they are best left to the experts. In Washington state, septic tanks get pumped whenever a home is transferred from one owner to another. The pumping company not only pumps the tanks, but tests the system and notes that each component is functioning properly. 99.9% of the time, this is done at the seller’s expense. In Thurston County, documents are sent to the county (with a fee of course) and reviewed. If everything is in order, a “time of transfer document” is issued and becomes part of the real estate transaction.
Some septic systems are older and pre-date permits and good record keeping. In that instance, pumpers will draw an “as built” which is what is on the site. This doesn’t mean that it functions any differently or is any less valuable.
Olympia Real Estate Blog 