The right of action of the county, its successors or assigns, under RCW 36.35.160 through 36.35.270 shall rest on the validity of the taxes involved, and the plaintiff shall be required to prove only the amount of the former judgment foreclosing the lien thereof, together with the costs of the foreclosure and sale of each tract of land for the taxes, and all the presumptions in favor of the tax foreclosure sale and issuance of treasurer's deed existing by law shall obtain in the action.